🧪 Bump setuptools in smoke test to v75.8.0

Previously GitHub updated their `ubuntu-latest` images to use Ubuntu
24.04 which has Python 3.12 as the default interpreter. Before that,
it was Ubuntu 22.04 with Python 3.9. This caused an uncontrolled
runtime bump which led to an incompatibility discovery — older
versions of `setuptools` are incompatible with Python 3.12.

This bumps the `setuptools` version following the previous commit
da900af that pins the distro version.
Going forward, these two must be bumped in tandem to avoid situations
when one gets upgraded suddenly but the other doesn't.

.github/workflows/reusable-smoke-test.yml

@@ -92,7 +92,7 @@ jobs:
         CONTENTS: |
           [build-system]
           requires = [
-            "setuptools == 65.6.3",
+            "setuptools == 75.8.0",
           ]
           build-backend = "setuptools.build_meta"