Fix Forgejo hostname resolution: set GITHUB_SERVER_URL to reachable address

The runner container cannot resolve 'forgejo' Docker hostname.
Set GITHUB_SERVER_URL to the accessible URL (10.100.0.2:3000).

- Add FORGEJO_URL env var (defaults to http://10.100.0.2:3000)
- Override GITHUB_SERVER_URL for checkout action
- Can be configured via vars.FORGEJO_URL in Forgejo settings

.forgejo/workflows/ci.yaml

@@ -15,6 +15,8 @@ jobs:
     runs-on: docker
     container:
       image: catthehacker/ubuntu:act-latest
+    env:
+      GITHUB_SERVER_URL: ${{ vars.FORGEJO_URL || 'http://10.100.0.2:3000' }}
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python
@@ -34,6 +36,8 @@ jobs:
     runs-on: docker
     container:
       image: catthehacker/ubuntu:act-latest
+    env:
+      GITHUB_SERVER_URL: ${{ vars.FORGEJO_URL || 'http://10.100.0.2:3000' }}
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python
@@ -51,6 +55,8 @@ jobs:
     runs-on: docker
     container:
       image: catthehacker/ubuntu:act-latest
+    env:
+      GITHUB_SERVER_URL: ${{ vars.FORGEJO_URL || 'http://10.100.0.2:3000' }}
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python