“Filter branches by name” checks fail

### Jenkins and plugins versions report

Environment

```text
Jenkins: 2.387.1
OS: Linux - 3.10.0-1160.62.1.el7.x86_64
Java: 11.0.18 - Red Hat, Inc. (OpenJDK 64-Bit Server VM)
---
gitlab-plugin:1.7.9
```

### What Operating System are you using (both controller, and any agents involved in the problem)?

CentOS 7

### Reproduction steps

1. Create a new job
2. In the build trigger “Filter branches by name” section, add any string to any text field.

### Expected Results

The branch names are correctly checked/autocompleted.

### Actual Results

An error message appears beneath the text field:


The log contains errors like these and stacktraces.
```
Error while serving https://my.jenkins.url.io/job/test%20job/descriptorByName/com.dabsquared.gitlabjenkins.GitLabPushTrigger/autoCompleteIncludeBranchesSpec
Error while serving https://my.jenkins.url.io/job/test%20job/descriptorByName/com.dabsquared.gitlabjenkins.GitLabPushTrigger/checkIncludeBranchesSpec

### Anything else?

_No response_