Fix CI by running on Python 3.11 (#3984)

aiohttp doesn't yet support 3.12

.github/workflows/diff_shades.yml

@@ -22,7 +22,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v4
         with:
-          python-version: "*"
+          python-version: "3.11"
 
       - name: Install diff-shades and support dependencies
         run: |
@@ -59,7 +59,7 @@ jobs:
 
       - uses: actions/setup-python@v4
         with:
-          python-version: "*"
+          python-version: "3.11"
 
       - name: Install diff-shades and support dependencies
         run: |

.github/workflows/doc.yml

@@ -26,7 +26,7 @@ jobs:
       - name: Set up latest Python
         uses: actions/setup-python@v4
         with:
-          python-version: "*"
+          python-version: "3.11"
 
       - name: Install dependencies
         run: |

.github/workflows/lint.yml

@@ -26,7 +26,7 @@ jobs:
       - name: Set up latest Python
         uses: actions/setup-python@v4
         with:
-          python-version: "*"
+          python-version: "3.11"
 
       - name: Install dependencies
         run: |