Tokens and password stored in plaintext!

### Jenkins and plugins versions report

Environment

```Jenkins: 2.452.1
OS: Linux - 4.15.0-225-generic
Java: 21.0.3 - Eclipse Adoptium (OpenJDK 64-Bit Server VM)
---
```

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

Ubuntu

### Reproduction steps

1. Go to https://plugins.jenkins.io/github-pr-coverage-status/
2. Read the security error

Optional:
3. Open com.github.terma.jenkins.githubprcoveragestatus.Configuration.xml
4. Note that your personal access token is indeed stored in plaintext

### Expected Results

My precious secrets to be encrypted and not stored in plaintext

### Actual Results

My precious secrets were stored in plaintext

### Anything else?

This deserves it's own patch. This is critically important.

### Are you interested in contributing a fix?

_No response_