Add GPG passphrase server entry to release settings.xml

The maven-gpg-plugin reads the passphrase from a settings.xml server
entry with id gpg.passphrase. Our custom settings.xml was missing this,
causing GPG to fail with "no terminal at all requested - can't get
input". The original setup-java action generated this entry
automatically, but we overwrote the settings.xml.

Author: mihaimitrea-db

.github/workflows/release.yml

@@ -74,6 +74,10 @@ jobs:
                 <username>${{ secrets.MAVEN_CENTRAL_USERNAME }}</username>
                 <password>${{ secrets.MAVEN_CENTRAL_PASSWORD }}</password>
               </server>
+              <server>
+                <id>gpg.passphrase</id>
+                <passphrase>\${env.GPG_PASSPHRASE}</passphrase>
+              </server>
             </servers>
           </settings>
           EOF