fix: prevent publication with unsupported credential types

[pcanilho]

fixes: #347

What changed?

Unsupported credential types are now explicitly made incompatible with the github-checks-plugin to avoid downstream unexpected exceptions such as the one reported here.

With this change, the supported credential types are:

• GitHubAppCredentials
• VaultUsernamePasswordCredentialImpl

If an unsupported credential type is provided, an early return is done to avoid having to handle downstream exceptions caused by incompatible types. This means that all pipeline console log entries will be suppressed if the pipeline has not been configured with compatible credentials.

Testing done

Procedure
As extracted from here, I have ran the following command to both build & run the test suite:

$ mvn -Penable-jacoco clean verify -B -V -ntp

A regression test was also carried out in our internal Jenkins controller to assert that previous functionality based on the above described credential types is left unaffected.

### Submitter checklist
- [x] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [x] Ensure that the pull request title represents the desired changelog entry
- [x] Please describe what you did
- [x] Link to relevant issues in GitHub or Jira
- [x] Link to relevant pull requests, esp. upstream and downstream changes
- [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[timja]

i guess ok

[codecov]

Codecov Report

Merging #351 (0e877c2) into master (983fed5) will decrease coverage by 0.22%.
The diff coverage is 33.33%.

@@             Coverage Diff              @@
##             master     #351      +/-   ##
============================================
- Coverage     72.02%   71.80%   -0.22%     
  Complexity      162      162              
============================================
  Files            16       16              
  Lines           529      532       +3     
  Branches         50       51       +1     
============================================
+ Hits            381      382       +1     
- Misses          123      124       +1     
- Partials         25       26       +1     

Impacted Files	Coverage Δ
...s/plugins/checks/github/GitHubChecksPublisher.java	94.54% <33.33%> (-3.54%)	⬇️

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[meiswjn]

To restore the previous behaviour it may be cleaner to put it here: https://github.com/jenkinsci/github-checks-plugin/blob/master/src/main/java/io/jenkins/plugins/checks/github/SCMFacade.java#L125-L134

[meiswjn]

Can this be merged? :) @timja

[timja]

heh I was giving @uhafner time to review as he seemed to get annoyed last time I merged same day.