Skip GPG signing in non-release builds

Author: atextor

.github/workflows/pull_request_check.yml

@@ -16,4 +16,4 @@ jobs:
         distribution: 'temurin'
         java-version: '17'
     - name: Run tests
-      run: mvn -B clean install
+      run: mvn -B clean install -Dgpg.skip=true

.github/workflows/release-workflow.yml

@@ -67,7 +67,7 @@ jobs:
             git push origin ${{ env.release_branch_name }}
           fi
       - name: Run tests and build
-        run: mvn -B clean install
+        run: mvn -B clean install -Dgpg.skip=true
 
       # release-build
       - name: Create GitHub release