chore(ci): pin reusable workflow to runcycles/.github@v1

Replaces the mutable `@main` ref on the reusable `ci-python.yml`
workflow with the stable `v1` tag cut from runcycles/.github after
PR #64 landed.

Brings the org-internal supply-chain posture in line with the pinned-SHA
posture already in use for third-party actions in this repo's
python-publish.yml. Within the v1 line the tag moves for
backward-compatible changes; breaking changes will bump to v2 with a
matching Dependabot bump here.

Closes runcycles/.github#60 (for this repo).

Author: amavashev

.github/workflows/ci.yml

@@ -11,6 +11,6 @@ permissions:
 
 jobs:
   ci:
-    uses: runcycles/.github/.github/workflows/ci-python.yml@main
+    uses: runcycles/.github/.github/workflows/ci-python.yml@v1
     with:
       mypy-target: runcycles