ci(release): run gradlew chmod inside the mod working-directory

The exec-bit step chmod'd ./gradlew from the repo root where the wrapper
does not exist, failing the release within seconds. Point it at mod/ like
the build step already does.

.github/workflows/release.yml

@@ -25,6 +25,7 @@ jobs:
           java-version: '25'
 
       - name: Grant the Gradle wrapper the exec bit
+        working-directory: mod
         run: chmod +x ./gradlew
 
       - name: Build the mod