.github: bump GitHub Actions to latest releases

Update pinned action revisions to the current upstream releases:

  actions/checkout      v6.0.2 -> v7.0.1
  actions/setup-python  v6.2.0 -> v7.0.0

Also switch the manually dispatched "test" workflow off the retired
ubuntu-20.04 runner image, which no longer exists on GitHub-hosted
runners, so the job can be started again.

Note that the workflow still calls docker-compose (v1), which is not
available on current runner images; that is left for a separate change.

Author: nuclearcat

.github/workflows/main.yml

@@ -26,10 +26,10 @@ jobs:
     steps:
 
       - name: Check out source code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Set up Python
-        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
         with:
           python-version: ${{ matrix.python-version }}
 
@@ -76,10 +76,10 @@ jobs:
 
     steps:
       - name: Check out source code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Set up Python
-        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
         with:
           python-version: '3.10'
 

.github/workflows/test.yml

@@ -16,7 +16,7 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
 
     strategy:
       matrix:
@@ -25,7 +25,7 @@ jobs:
     steps:
 
       - name: Check out source code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Export environment variables
         run: |