ci(test): use apt-get with correct Ubuntu packages in workflow

Replace Alpine-style commands (apk, py3-pip, musl-dev) and incorrect
apt usage with proper apt-get invocations and Debian package names for
the ubuntu-latest runner.

.gitea/workflows/test.yaml

@@ -16,7 +16,7 @@ jobs:
       - name: Install system dependencies
         shell: sh
         run: |
-          apt upgrade && apt install git python3 py3-pip gcc musl-dev libpq-dev python3-dev
+          apt-get update && apt-get install -y git python3 python3-pip gcc libpq-dev python3-dev
 
       - name: Checkout code
         shell: sh
@@ -37,7 +37,7 @@ jobs:
       - name: Install Node.js and frontend dependencies
         shell: sh
         run: |
-          apk add --no-cache nodejs npm
+          apt-get install -y nodejs npm
           cd frontend && npm ci
 
       - name: Verify generated API types are up to date