check_patch_files.py fails when a release tag is also resolved as a path

[jpezzulli]

Problem

While regenerating the v0.24 patch, I ran:

VLLM_MOET_FORK=/opt/vllm-v0.24.0 \
python3 tools/check_patch_files.py --update

The checker failed when Git resolved v0.24.0 as both a revision and a path:

fatal: ambiguous argument 'v0.24.0': both revision and filename
Use '--' to separate paths from revisions

The affected calls on current main are the two source-diff operations in tools/check_patch_files.py.

Proposed fix

Terminate the revision arguments with --:

regen = git(fork, "diff", BASE_TAG, sha, "--").stdout

and:

diff = git(fork, "diff", BASE_TAG, new, "--").stdout

After making those two changes locally, --update completed successfully:

patch file list OK (68 files)
patch source OK: byte-identical to `git diff v0.24.0 0156788a9cb8` in /opt/vllm-v0.24.0

PR #11 rewrites this checker for multiple releases but retains equivalent unseparated git diff calls. If that PR is updated, the same -- separator should be added to both production calls and to the raw-diff command in tests/test_check_patch_files.py.

A regression test can create a path named v0.25.0 alongside the v0.25.0 tag and verify that source checking and regeneration still succeed.