Let all tests complete if one fails

Typically, when one fails, the others are at least 90% done, so there isn't much saving in failing fast.
I would rather see if the failure is for all py versions or just some.

.github/workflows/testing.yml

@@ -101,6 +101,7 @@ jobs:
     needs: [poetry-lock]
     runs-on: ubuntu-latest
     strategy:
+      fail-fast: false
       matrix:
         python-version: ["3.11", "3.12", "3.13"]
     steps: