Test runner warns of missing basline for performance tests with expected changes

When the commit message documents expected performance tests changes, the test runner warns of missing baselines for those tests, but a baseline is not needed, so the warning should ignore such cases.

an example: https://gitlab.haskell.org/ghc/ghc/-/jobs/34315

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Test Suite
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import testsuite labels

mentioned in commit 6c4e45b0

added Pnormal label

@DavidEichmann Can this be closed, since 6c4e45b0 is in master?

added perf tests label

@monoidal Indeed. Thanks for pointing this out.

closed