CI failures due to `main` vs `master` branches in LibGit2 tests on macOS

[tkf]

I see failures like https://build.julialang.org/#/builders/2/builds/3456/steps/5/logs/stdio

Error in testset LibGit2/libgit2:
Test Failed at /Users/julia/buildbot/worker-tabularasa/tester_macos64/build/share/julia/stdlib/v1.9/LibGit2/test/libgit2.jl:961
  Expression: LibGit2.name(brref) == "refs/heads/master"
   Evaluated: "refs/heads/main" == "refs/heads/master"

I don't know if it is macOS-specific but I notice it only on macOS. I'm also not sure if it occurs always.