github: stop testing cli against Python 3.8 now that core22 provides …

…3.10

Signed-off-by: Simon Deziel <simon.deziel@canonical.com>

.github/workflows/cli-tox.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: [self-hosted, linux, X64]
     strategy:
       matrix:
-        python: ["3.8", "3.10"]
+        python: ["3.10"]
     steps:
     - uses: actions/checkout@v4
     - name: Set up Python