Configuration ignores app credential override

### Jenkins and plugins versions report

Environment

```text
Jenkins: 2.401.3
OS: Linux - 5.4.0-1093-aws
Java: 11.0.19 - Eclipse Adoptium (OpenJDK 64-Bit Server VM)

github-checks:545.v79a_a_68b_ca_682
```

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

Ubuntu 18 for the agents and the controller

### Reproduction steps

1. Set up a job to use SSH credentials to pull from GitHub
2. In the GitHub checks configuration, override the credentials to point to app credentials
3. Stop a job while it's building
4. After the first job failure all subsequent jobs fail to report the build result to GitHub with the error:
```
[GitHub Checks] Failed Publishing GitHub checks: java.io.IOException: Unsupported credential type: com.cloudbees.jenkins.plugins.sshcredentials.impl.BasicSSHUserPrivateKey
```
Which means it is ignoring the credential override after the first failure.

### Expected Results

All jobs should be using the override for the credential id, instead of the credentials used to pull the code.

### Actual Results

```
[GitHub Checks] Failed Publishing GitHub checks: java.io.IOException: Unsupported credential type: com.cloudbees.jenkins.plugins.sshcredentials.impl.BasicSSHUserPrivateKey
```
Presumably using the wrong credentials.

### Anything else?

I suspect the problem started with https://github.com/jenkinsci/github-checks-plugin/pull/341/files
Specifically, I think `findGitHubAppCredentials` is returning the first credentials (SSH Key type) instead of the app credentials configured: https://github.com/jenkinsci/github-checks-plugin/blob/8d1713321e3db97eb07ff398400fb80efc5f6c24/src/main/java/io/jenkins/plugins/checks/github/SCMFacade.java#L126