No Creditials Found exception in addGitLabMRComment

## I just tried to add Merge request comments to my Merge pipeline, and while updateGitlabCommitStatus in line just above it is successful, addGitlabMRComment causes an IllegalStateException: No credentials found for credentialsId

### Context
- **Gitlab plugin version**: 1.5.19
- **Gitlab version**: 13.8.4
- **Jenkins version**: 2.263.4
- **Job type**: Pipeline

### Logs & Traces

the actual exception is:
```
java.lang.IllegalStateException: No credentials found for credentialsId:
at com.dabsquared.gitlabjenkins.connection.GitLabConnection.getApiToken(GitLabConnection.java:155)
at com.dabsquared.gitlabjenkins.connection.GitLabConnection.getClient(GitLabConnection.java:131)
at com.dabsquared.gitlabjenkins.connection.GitLabConnectionConfig.getClient(GitLabConnectionConfig.java:66)
at com.dabsquared.gitlabjenkins.connection.GitLabConnectionProperty.getClient(GitLabConnectionProperty.java:74)
at com.dabsquared.gitlabjenkins.connection.GitLabConnectionProperty.getClient(GitLabConnectionProperty.java:85)
at com.dabsquared.gitlabjenkins.workflow.AddGitLabMergeRequestCommentStep$AddGitLabMergeRequestCommentStepExecution.run(AddGitLabMergeRequestCommentStep.java:79)
at com.dabsquared.gitlabjenkins.workflow.AddGitLabMergeRequestCommentStep$AddGitLabMergeRequestCommentStepExecution.run(AddGitLabMergeRequestCommentStep.java:60)
at org.jenkinsci.plugins.workflow.steps.AbstractSynchronousStepExecution.start(AbstractSynchronousStepExecution.java:42)
at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:319)
at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:193)
at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:122)
at sun.reflect.GeneratedMethodAccessor192.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:42)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:163)
at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:157)
at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:161)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:165)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:135)
at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)
at WorkflowScript.run(WorkflowScript:255)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.delegateAndExecute(ModelInterpreter.groovy:137)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.runPostConditions(ModelInterpreter.groovy:756)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.catchRequiredContextForNode(ModelInterpreter.groovy:395)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.catchRequiredContextForNode(ModelInterpreter.groovy:393)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.runPostConditions(ModelInterpreter.groovy:755)
at com.cloudbees.groovy.cps.CpsDefaultGroovyMethods.each(CpsDefaultGroovyMethods:2030)
at com.cloudbees.groovy.cps.CpsDefaultGroovyMethods.each(CpsDefaultGroovyMethods:2015)
at com.cloudbees.groovy.cps.CpsDefaultGroovyMethods.each(CpsDefaultGroovyMethods:2056)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.runPostConditions(ModelInterpreter.groovy:745)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.runPostConditions(ModelInterpreter.groovy)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.executePostBuild(ModelInterpreter.groovy:723)
at ___cps.transform___(Native Method)
at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:86)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:113)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
at sun.reflect.GeneratedMethodAccessor159.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.CollectionLiteralBlock$ContinuationImpl.dispatch(CollectionLiteralBlock.java:55)
at com.cloudbees.groovy.cps.impl.CollectionLiteralBlock$ContinuationImpl.item(CollectionLiteralBlock.java:45)
at sun.reflect.GeneratedMethodAccessor176.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:107)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
at sun.reflect.GeneratedMethodAccessor159.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:89)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:113)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
at sun.reflect.GeneratedMethodAccessor159.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.ConstantBlock.eval(ConstantBlock.java:21)
at com.cloudbees.groovy.cps.Next.step(Next.java:83)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:174)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:163)
at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:129)
at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:268)
at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:163)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:185)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:400)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$400(CpsThreadGroup.java:96)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:312)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:276)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:136)
at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:59)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

```

### Problem description

the test pipeline fails on the merge step and should update add a comment to the Gitlab Merge Request. this fails cause of the exception above.