Add a few more commits to `.git-blame-ignore-rev`

[jieyouxu]

When I was doing git archaeology in the tests/ repo, I noticed there's a couple of commits that probably should be added to .git-blame-ignore-rev because they're like moving tests around and things.

[ranger-ross]

Spent some time looking through the tests commits and compiled a list of candidates that I noticed.

• 141d9dc -- remove unused imports from rmake tests
• d6a9ad6 -- remove unused imports from rmake tests
• c9c80d2 -- rustfmt tests/mir-opt
• 22ed23d -- Convert lldbg- to lldb-
• 99cb0c6 -- Bless all the mir-opt tests
• d562a4a -- renamed .output() to .out_dir()