workflows: Remove python 3.7 from matrix

Python 3.7 is EOL and since we're using importlib.metadata which
is only included starting 3.8 then dropping that release from
the test matrix.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>

.github/workflows/pull_request.yml

@@ -107,7 +107,7 @@ jobs:
     strategy:
       matrix:
         os-version: ["ubuntu-22.04"]
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
     runs-on: "${{ matrix.os-version }}"
     steps:
       - name: Checkout