switch to use server's new actions org

.forgejo/workflows/checks.yml

@@ -6,7 +6,7 @@ jobs:
   checks:
     runs-on: debian-12
     steps:
-      - uses: https://git.libre-chip.org/mirrors/checkout@v4
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
           submodules: true
@@ -19,7 +19,7 @@ jobs:
               default-jre-headless \
               jq \
               python3-venv
-      - uses: https://git.libre-chip.org/mirrors/cache@v4
+      - uses: actions/cache@v4
         with:
           path: ~/.m2/repository
           key: maven-repository