Use minimum supported Python 3.8 over default x-range which points to…

… Python 3.7

See #15851 (comment)

.github/workflows/release-artifacts.yml

@@ -30,7 +30,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
         with:
-          python-version: '3.x'
+          python-version: '3.8'
       - id: set-distros
         run: |
           # if we're running from a tag, get the full list of distros; otherwise just use debian:sid
@@ -76,7 +76,7 @@ jobs:
       - name: Set up python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.x'
+          python-version: '3.8'
 
       - name: Build the packages
         # see https://github.com/docker/build-push-action/issues/252
@@ -125,9 +125,10 @@ jobs:
 
       - uses: actions/setup-python@v4
         with:
-          # setup-python@v4 doesn't impose a default python version. Need to use 3.x
-          # here, because `python` on osx points to Python 2.7.
-          python-version: "3.x"
+          # setup-python@v4 doesn't impose a default python version. We define a version
+          # here because `python` on osx points to Python 2.7. We use the minimium
+          # supported Python version that Synapse supports.
+          python-version: "3.8"
 
       - name: Install cibuildwheel
         run: python -m pip install cibuildwheel==2.9.0