Improve rename detection

[lrbison]

Improve rename detection by increasing diff.renameLimit

An proposed change to address #1

[haampie]

Maybe better to run git -c "diff.renamelimit=<something large>" to avoid changing user config

[haampie]

fwiw, I cannot reproduce with git version 2.39.5:

% migrate-pkg-prs 49641
Pull requests {#49641} are copied to local branches
Fetching spack/spack-packages's develop branch...
From https://github.com/spack/spack-packages
 * [new branch]            develop    -> spack-packages-develop
Fetching spack/spack's develop branch...
remote: Enumerating objects: 641860, done.
remote: Counting objects: 100% (473/473), done.
remote: Compressing objects: 100% (285/285), done.
remote: Total 641860 (delta 308), reused 195 (delta 179), pack-reused 641387 (from 3)
Receiving objects: 100% (641860/641860), 217.73 MiB | 34.54 MiB/s, done.
Resolving deltas: 100% (301106/301106), done.
From https://github.com/spack/spack
 * [new branch]              develop    -> spack-develop
Processing 1 pull requests
[1/1] 'gcc: run mkheaders after buildcache install' (#49641): local branch spack-pr-49641
Summary: copied 1 and skipped 0

where git config diff.renameLimit exits with code 1

[lrbison]

Interesting. Well then no hurry to merge it. If others have problems perhaps they will chime in otherwise we can close the issue and PR as something unique to my setup.