Use nightlies for gz-harmonic (#66)

* Use nightlies for Harmonic

* Update Actions and python versions

Python 3.6 is not available in ubuntu-latest (22.04).

* Quote python versions

See actions/runner#1989


---------

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

.github/workflows/main.yml

@@ -9,12 +9,12 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.8]
+        python-version: ['3.8', '3.10']
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies

plugins/config/repository.yaml

@@ -24,6 +24,13 @@ repositories:
 # wildcards are allowed in name, entries are processed in top-down order
 # first entry matching the name is used
 projects:
+    # Remove gz-harmonic1 when Harmonic is released
+    - name: gz-harmonic1
+      repositories:
+          - name: osrf
+            type: stable
+          - name: osrf
+            type: nightly
     # Use nightlies in all main branches
     - name: gz-cmake4
       repositories: