Revert "ci: Update Python versions to range 3.8 .. 3.12"

This reverts commit 4c2c1b9.

aiohttp is not Python 3.12 ready yet: aio-libs/aiohttp#7646

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.8", "3.10", "3.12"]
+        python-version: ["3.7", "3.9", "3.11"]
 
     steps:
     - uses: actions/checkout@v2
@@ -50,10 +50,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.12
+    - name: Set up Python 3.11
       uses: actions/setup-python@v2
       with:
-        python-version: "3.12"
+        python-version: "3.11"
     - name: Install Python dependencies
       run: |
         python -m pip install --upgrade pip
@@ -71,10 +71,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.12
+    - name: Set up Python 3.11
       uses: actions/setup-python@v2
       with:
-        python-version: "3.12"
+        python-version: "3.11"
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip