fix(ci): Provide GPG passphrase environment variable to setup-java

The MAVEN_GPG_PASSPHRASE environment variable must be available at the
setup-java step level for GPG key import to work. Previously it was only
set for the Maven publish step, causing "exit code 2" errors during both
GPG import and cleanup.

Also added diagnostic step to verify GPG key format.

Author: schrepfler

.github/workflows/maven-publish.yml

@@ -36,6 +36,8 @@ jobs:
         server-password: MAVEN_PASSWORD                       # env variable for token in deploy
         gpg-private-key: ${{ secrets.OSSRH_GPG_SECRET_KEY }}  # Value of the GPG private key to import
         gpg-passphrase: MAVEN_GPG_PASSPHRASE                  # env variable for GPG private key passphrase
+      env:
+        MAVEN_GPG_PASSPHRASE: ${{ secrets.OSSRH_GPG_SECRET_KEY_PASSWORD }}
 
     - name: Publish package
       run: mvn --no-transfer-progress --batch-mode -DperformRelease=true clean deploy