Port multiloader build to Fabric and Forge 1.20.1

.gitea/workflows/build.yml

@@ -2,7 +2,7 @@ name: Build
 
 on:
   push:
-    branches: [main]
+    branches: [main, multiloader]
   pull_request:
 
 env:
@@ -25,7 +25,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: '21'
+          java-version: '17'
           cache: gradle
       - run: chmod +x ./gradlew
       - run: ./gradlew build --no-daemon