chore: downgrade Python version to 3.9 in workflows and configuration files

Author: dermatologist

.github/workflows/pr.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: ["3.11"]
+        python-version: ["3.9"]
         os: [ubuntu-latest, macos-13, windows-latest]
     runs-on: ${{ matrix.os }}
     timeout-minutes: 20

.github/workflows/tox.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: ["3.11"]
+        python-version: ["3.9"]
 
     steps:
     - uses: actions/checkout@v4

.readthedocs.yml

@@ -19,7 +19,7 @@ formats:
 build:
   os: ubuntu-22.04
   tools:
-    python: "3.11"
+    python: "3.9"
 
 python:
   install: