try to prevent settings.xml from being overwritten

The setup-java action changes the server id to "ossrh" but
"Failed to decrypt password for server github" is a clue that
settings.xml was reverted back to its previous state where
the id was "github".

This issue seems related:
actions/cache#1195

.github/workflows/maven-snapshot.yml

@@ -23,7 +23,7 @@ jobs:
             - name: Cache Maven packages
               uses: actions/cache@v4
               with:
-                  path: ~/.m2
+                  path: ~/.m2/repository
                   key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
                   restore-keys: ${{ runner.os }}-m2
             - name: Build, test, verify and publish snapshot