Rename label "merge-ready" to "full-build" (#679 / #682)

[nipafx]

Switching from the reduced, faster build to the full build of all Java/OS/etc combinations requires adding a specific label to the PR. It was called "merge-ready", which marks the PR as being ready to be merged once the build is green, but that is (at least) occasionally not the case.

To avoid confusion, we rename the label to the less leading name "full-build".

Proposed commit message:

Rename label "merge-ready" to "full-build" (#679 / #682)
    
Switching from the reduced, faster build to the full build of all
Java/OS/etc combinations requires adding a specific label to the PR.
It was called "merge-ready", which marks the PR as being ready to be
merged once the build is green, but that is (at least) occasionally
not the case.
    
To avoid confusion, we rename the label to the less leading name
"full-build".
    
Closes: #679
PR: #682

---

PR checklist

The following checklist shall help the PR's author, the reviewers and maintainers to ensure the quality of this project.
It is based on our contributors guidelines, especially the "writing code" section.
It shall help to check for completion of the listed points.
If a point does not apply to the given PR's changes, the corresponding entry can be simply marked as done.

Documentation (general)

• There is documentation (Javadoc and site documentation; added or updated)
• There is implementation information to describe why a non-obvious source code / solution got implemented
• Site documentation has its own .adoc file in the docs folder, e.g. docs/report-entries.adoc
• Site documentation in .adoc file references demo in src/demo/java instead of containing code blocks as text
• Only one sentence per line (especially in .adoc files)
• Javadoc uses formal style, while sites documentation may use informal style

Documentation (new extension)

• The docs/docs-nav.yml navigation has an entry for the new extension
• The package-info.java contains information about the new extension

Code

• Code adheres to code style, naming conventions etc.
• Successful tests cover all changes
• There are checks which validate correct / false usage / configuration of a functionality and there are tests to verify those checks
• Tests use AssertJ or our own PioneerAssert (which are based on AssertJ)

Contributing

• A prepared commit message exists
• The list of contributions inside README.md mentions the new contribution (real name optional)

[nipafx]

⚠️ THE LABEL IS NOT YET RENAMED ⚠️

The label needs to be actually renamed when this PR gets merged ~> https://github.com/junit-pioneer/junit-pioneer/labels