build: macos-13 is needed for older Pythons

While we're here, update to latest versions of actions.

.github/workflows/ci.yml

@@ -18,15 +18,15 @@ concurrency:
 jobs:
   tests:
     name: "Python ${{ matrix.python }} on ${{ matrix.os }}"
-    runs-on: "${{ matrix.os }}"
+    runs-on: "${{ matrix.os }}-${{ matrix.os-version || 'latest' }}"
 
     strategy:
       fail-fast: false
       matrix:
         os:
-          - ubuntu-latest
-          - macos-latest
-          - windows-latest
+          - ubuntu
+          - macos
+          - windows
         python:
           # When changing this list, be sure to check the [gh] list in
           # tox.ini so that tox will run properly.
@@ -36,13 +36,23 @@ jobs:
           - "3.10"
           - "3.11"
           - "3.12"
+        include:
+          - python: "3.7"
+            os: "macos"
+            os-version: "13"
+          - python: "3.8"
+            os: "macos"
+            os-version: "13"
+          - python: "3.9"
+            os: "macos"
+            os-version: "13"
 
     steps:
       - name: "Check out the repo"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v4"
 
       - name: "Set up Python"
-        uses: "actions/setup-python@v2"
+        uses: "actions/setup-python@v5"
         with:
           python-version: "${{ matrix.python }}"
 
@@ -68,12 +78,12 @@ jobs:
 
     steps:
       - name: "Check out the repo"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v4"
         with:
           fetch-depth: "0"
 
       - name: "Set up Python"
-        uses: "actions/setup-python@v2"
+        uses: "actions/setup-python@v5"
         with:
           python-version: "3.8"
 
@@ -82,7 +92,7 @@ jobs:
           python -m pip install -r requirements.pip
 
       - name: "Download coverage data"
-        uses: actions/download-artifact@v2
+        uses: actions/download-artifact@v4
         with:
           name: covdata