This is an upstream Guix issue (55273), but they seem to be planning to resolve it with a version bump, and either way we have versions pinned I think.
0building /gnu/store/myai2xf4f0z2nr331mx2y4xr4jv1lwid-libgit2-1.3.0.drv...
1| 'unpack' phaseild-log 356 178
2`/gnu/store/xa8yg9nvawhfvk6hv8lhif9z5pybzan5-libgit2-1.3.0-checkout/tests/resources/status/staged_delete_modified_file' -> `./tests/resources/status/staged_delete_modified_file'
3 17% [######################## ]ild-log 356 189
4/tmp/guix-build-libgit2-1.3.0.drv-0/source/src/regexp.c:148:5: warning: ?error? may be used uninitialized in this function [-Wmaybe-uninitialized]
5 148 | if (error < 0)
6 | ^
7 17% [######################## ]ild-log 356 72
8[ 18%] Building C object src/CMakeFiles/git2internal.dir/repository.c.o
9| 'check' phasenote: keeping build directory `/tmp/guix-build-libgit2-1.3.0.drv-0'
10builder for `/gnu/store/myai2xf4f0z2nr331mx2y4xr4jv1lwid-libgit2-1.3.0.drv' failed with exit code 1
11build of /gnu/store/myai2xf4f0z2nr331mx2y4xr4jv1lwid-libgit2-1.3.0.drv failed
0refs::revparse.................F
1
2 1) Failure:
3refs::revparse::date [/tmp/guix-build-libgit2-1.3.0.drv-0/source/tests/refs/revparse.c:31]
4 Function call succeeded: error
5 no error, expected non-zero return