[3.0.x] Tests for swagger-generator fail on windows

Description

I´m trying to build swagger-codegen from source, but the tests for swagger-generator fail with

ERROR i.s.v.g.u.FileAccessSecurityManager - Exception getting absolute path for file C:\Users\nils-\AppData\Local\Temp\codegen-10411439581359926604\_..\mytemp and/or allowed dir
java.io.IOException: Das System kann den angegebenen Pfad nicht finden
        at java.base/java.io.WinNTFileSystem.canonicalize0(Native Method)
        at java.base/java.io.WinNTFileSystem.canonicalize(WinNTFileSystem.java:438)
        at java.base/java.io.File.getCanonicalPath(File.java:620)
        at io.swagger.v3.generator.util.FileAccessSecurityManager.checkWrite(FileAccessSecurityManager.java:33)
        at java.base/java.io.File.mkdir(File.java:1325)
        at java.base/java.io.File.mkdirs(File.java:1357)
        at io.swagger.codegen.AbstractGenerator.writeToFile(AbstractGenerator.java:30)
        at io.swagger.codegen.DefaultGenerator.generateSupportingFiles(DefaultGenerator.java:638)
        at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:781)
        at io.swagger.codegen.v3.service.GeneratorService.generate(GeneratorService.java:50)
        at io.swagger.v3.generator.online.GeneratorController.generate(GeneratorController.java:508)
        at io.swagger.v3.generator.online.GeneratorController.generate(GeneratorController.java:476)
        at io.swagger.v3.generator.online.GeneratorControllerTest.generateBashWithAndWithoutSecurityThreat(GeneratorControllerTest.java:86)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
...

followed by

ERROR i.s.v.g.online.GeneratorController - Error generating `bash` code : Could not generate supporting file 'SupportingFile:
        templateFile: zsh-completion.mustache
        folder:
        destinationFilename: _../mytemp/start
'
java.lang.RuntimeException: Could not generate supporting file 'SupportingFile:
        templateFile: zsh-completion.mustache
        folder:
        destinationFilename: _../mytemp/start

and

Caused by: java.lang.SecurityException: Exception getting absolute path for allowed dir C:\Users\nils-\AppData\Local\Temp\ and/or file C:\Users\nils-\AppData\Local\Temp\codegen-10411439581359926604\_..\
mytemp
        at io.swagger.v3.generator.util.FileAccessSecurityManager.checkWrite(FileAccessSecurityManager.java:38)
        at java.base/java.io.File.mkdir(File.java:1325)
        at java.base/java.io.File.mkdirs(File.java:1357)
        at io.swagger.codegen.AbstractGenerator.writeToFile(AbstractGenerator.java:30)
        at io.swagger.codegen.DefaultGenerator.generateSupportingFiles(DefaultGenerator.java:638)
        ... 34 common frames omitted

when running mvn clean package. Skipping the tests with -DskipTests does work as a workaround.

Looking through the source code, theres a System.setSecurityManager(new FileAccessSecurityManager()); at line 58 in GeneratorController.java. Deactivating that did remove the SecurityException, but the

ERROR i.s.v.g.online.GeneratorController - Error generating `bash` code : Could not generate supporting file 'SupportingFile:
        ...
'
java.lang.RuntimeException: Could not generate supporting file 'SupportingFile:
       ...

were still there.
The codegen-10411439581359926604 folder under Temp/ does exist, so it was able to create it, but the _.. folder from that path does not.

Swagger-codegen version

Tested with tags v3.0.25, v3.0.26 and branch 3.0.0.

Command line used for generation

mvn clean package
Maven 3.6.3
AdoptOpenJDK 11

Steps to reproduce

Run mvn clean package on one of the above mentioned tags/branches.

Start with GeneratorController.java around line 58 and inspect FileAccessSecurityManager.java, then review GeneratorControllerTest.java around line 86. Run mvn clean package on Windows using the reported Java and Maven versions. Done means the swagger-generator tests complete without the path-related SecurityException or supporting-file generation error.