GH CI is skipping all ITs: needs system prerequisites

### Affected version

master

### Bug description

as seen in #152 , current GH Actions run skips every IT:
```
[INFO] -------------------------------------------------
[INFO] Build Summary:
[INFO] Passed: 0, Failed: 0, Errors: 0, Skipped: 5
[INFO] -------------------------------------------------
Warning: The following builds were skipped:
Warning: * publish-scm-staged/pom.xml
Warning: * issue-mscmpub-50/pom.xml
Warning: * site-deploy/pom.xml
Warning: * publish-scm-skip/pom.xml
Warning: * publish-scm/pom.xml
[INFO] -------------------------------------------------
```

then does not detect any failure, like with Maven 4

need to install system `svn` and `svnadmin` prerequisites to avoid skipping ITs: https://github.com/apache/maven-scm-publish-plugin/blob/master/src/it/publish-scm/selector.groovy

Inspect the GitHub Actions setup and the integration-test selector at src/it/publish-scm/selector.groovy, then reproduce the current run to confirm the ITs are skipped. Ensure the CI environment provides the stated system prerequisites and verify that the five builds execute and failures are detected.

Written by the indexing model from the issue text.