feat: Replace 'test' job with 'build' job in Forgejo workflows

- Jobs in Forgejo workflows are updated to remove the 'test' job and expand the 'build' job.
- This is performed to streamline the workflows and employ a more central build job instead of individual testing ones.
- Also, the 'nix build' command is updated in the 'build' job for proper syntax.

.forgejo/workflows/nix.yaml

@@ -1,15 +1,7 @@
 on: [push]
 jobs:
-  test:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - run: |
-          pwd
-          ls -al
-
   build:
     runs-on: nix
     steps:
       - uses: actions/checkout@v3
-      - run: nix build -L .runner
+      - run: nix build -L .#runner