`Tests / Change detection` fails consistently for `3.14` branch

[sobolevn]

Bug report

Link: https://github.com/python/cpython/actions/runs/15038350621/job/42264238017

Run python Tools/build/compute-changes.py
##[debug]/usr/bin/bash -e /home/runner/work/_temp/b54cd67a-b3c1-4f7c-ae74-c2e1fd097e3c.sh
fatal: bad revision 'origin/main...f2a4b1066be66574a147bc353efc91a6dc65753d'
target ref: 'main'
head ref: 'f2a4b1066be66574a147bc353efc91a6dc65753d'
git diff --name-only origin/main...f2a4b1066be66574a147bc353efc91a6dc65753d --
Traceback (most recent call last):
  File "/home/runner/work/cpython/Tools/build/compute-changes.py", line 206, in <module>
    compute_changes()
    ~~~~~~~~~~~~~~~^^
  File "/home/runner/work/cpython/Tools/build/compute-changes.py", line 62, in compute_changes
    files = get_changed_files(target_branch, head_ref)
  File "/home/runner/work/cpython/Tools/build/compute-changes.py", line 107, in get_changed_files
    changed_files_result = subprocess.run(
        args, stdout=subprocess.PIPE, check=True, encoding="utf-8"
    )
  File "/opt/hostedtoolcache/Python/3.13.3/x64/lib/python3.13/subprocess.py", line 577, in run
    raise CalledProcessError(retcode, process.args,
                             output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '('git', 'diff', '--name-only', 'origin/main...f2a4b1066be66574a147bc353efc91a6dc65753d', '--')' returned non-zero exit status 128.

See other commits in the same branch: https://github.com/python/cpython/commits/3.14/

It is failing since 7504fe6

CC @hugovk @AA-Turner

[hugovk]

I already have a PR to fix this: #133671