LLVMFailGitHubReporter reports to a wrong MR in case of multiple MR numbers in the commit message

[gkistanova]

Please see https://github.com/llvm/llvm-project/pull/98851 for the example of commenting a wrong MR. Example of such commit message:

Reapply "AMDGPU: Move attributor into optimization pipeline (#83131)" and follow up commit "clang/AMDGPU: Defeat attribute optimization in attribute test" (#98851)

We should always parse the MR number at the end and ignore anything in the message body.