Update test action and Skript version in workflow

Author: devdinc

.github/workflows/test-skripts.yml

@@ -81,14 +81,14 @@ jobs:
           EOF
 
       - name: Run tests
-        uses: devdinc/skript-test-action@v1.3
+        uses: SkriptLang/skript-test-action@v1.3
         with:
           skript_repo_url: https://github.com/SkriptLang/Skript.git
           # directory where your test scripts are located (relative to repo root)
           test_script_directory: tests
 
           # Skript version or ref (tag, branch, or commit)
-          skript_repo_ref: 2.15.0-pre1
+          skript_repo_ref: 2.15.0
 
           # directory containing addon/plugin jars (relative to repo root)
           extra_plugins_directory: build/libs