gz-tools2: disable Ubuntu Focal CI (#169)

Removed focal CI job from GitHub Actions workflow.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

Author: scpeters

.github/workflows/ci.yml

@@ -9,15 +9,6 @@ on:
       - 'main'
 
 jobs:
-  focal-ci:
-    runs-on: ubuntu-latest
-    name: Ubuntu Focal CI
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-      - name: Compile and test
-        id: ci
-        uses: gazebo-tooling/action-gz-ci@focal
   jammy-ci:
     runs-on: ubuntu-latest
     name: Ubuntu Jammy CI