ci: swap fastapi with flask for test

fastapi requires setting a custom python version

Author: tagoro9

.github/workflows/ci.yaml

@@ -32,7 +32,7 @@ jobs:
     strategy:
       matrix:
         repos:
-          - tiangolo/fastapi
+          - pallets/flask
     steps:
       - uses: actions/checkout@v4
         with: