Unstable tests based on AssertRefLogEntry

Several tests are unstable and fail all too frequently on CI and perhaps locally.

From this run of this commit the windows agent happened to fail with this log:

  X LibGit2Sharp.Tests.BranchFixture.CanCreateBranchFromCommit [63ms]
  Error Message:
   Assert.InRange() Failure
Range:  (1/31/2020 4:54:25 AM +00:00 - 1/31/2020 4:54:25 AM +00:00)
Actual: 1/31/2020 4:54:24 AM +00:00
  Stack Trace:
     at LibGit2Sharp.Tests.TestHelpers.BaseFixture.AssertRefLogEntry(IRepository repo, String canonicalName, String message, ObjectId from, ObjectId to, Identity committer, DateTimeOffset before) in D:\a\libgit2sharp\libgit2sharp\LibGit2Sharp.Tests\TestHelpers\BaseFixture.cs:line 471
   at LibGit2Sharp.Tests.BranchFixture.CanCreateBranchFromCommit() in D:\a\libgit2sharp\libgit2sharp\LibGit2Sharp.Tests\BranchFixture.cs:line 205

It looks to me like the before local variable is still set to a later value than is recorded in the commit at times, for whatever reason.

Comece com AssertRefLogEntry em LibGit2Sharp.Tests/TestHelpers/BaseFixture.cs e com o teste com falha CanCreateBranchFromCommit em LibGit2Sharp.Tests/BranchFixture.cs. Execute o teste afetado repetidamente, inspecione a falha de CI referenciada e compare os timestamps esperados e registrados do reflog. Está concluído quando os testes afetados não falharem mais intermitentemente no CI ou localmente.