fix: remove explicit dorny base, rely on v3 default

dorny/paths-filter v3 already diffs against the repo default branch
for non-default-branch pushes. Explicit base: main was redundant and
would produce wrong baselines for backport PRs targeting release
branches (all files seen as changed vs main).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: cpcloud

.github/workflows/ci.yml

@@ -111,11 +111,10 @@ jobs:
         if: ${{ startsWith(github.ref_name, 'pull-request/') }}
         uses: dorny/paths-filter@d1c1ffe0248fe513906c8e24db8ea791d46f8590  # v3.0.3
         with:
-          # Explicitly compare against the repository default branch. On push
-          # events dorny/paths-filter defaults to diffing against the prior
-          # commit, which is wrong for backport PRs targeting non-default
-          # branches. Pinning base to main ensures consistent detection.
-          base: main
+          # dorny/paths-filter v3 on push to a non-default branch defaults to
+          # diffing against the repository default branch. No explicit base is
+          # needed; omitting it lets backport PRs targeting release branches
+          # diff against their actual target rather than always against main.
           filters: |
             bindings:
               - 'cuda_bindings/**'