Add GitHub workflow to build with Gradle.

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout sources
+      uses: actions/checkout@v2
+
+    - name: Set up JDK 14
+      uses: actions/setup-java@v1
+      with:
+        java-version: 14
+
+    - name: Cache Gradle packages
+      uses: actions/cache@v2
+      with:
+        path: ~/.gradle/caches
+        key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle') }}
+        restore-keys: ${{ runner.os }}-gradle
+
+    - name: Build with Gradle
+      run: ./gradlew build
+      env:
+        # Necessary to fetch Towny dependency from GitHub packages.
+        GITHUB_ACTOR: ${{ github.actor }}
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

build.gradle

@@ -26,8 +26,8 @@ repositories {
     name = "Towny"
     url = "https://maven.pkg.github.com/TownyAdvanced/Towny"
     credentials {
-      username = project.findProperty("gpr.user") ?: System.getenv("USERNAME")
-      password = project.findProperty("gpr.key") ?: System.getenv("TOKEN")
+      username = project.findProperty("gpr.user") ?: System.getenv("GITHUB_ACTOR")
+      password = project.findProperty("gpr.key") ?: System.getenv("GITHUB_TOKEN")
     }
   }
 }