regression: `testament r filename` (etc) fails (pcat still works)

[timotheecour]

regression introduced in #16698 /cc @xflywind

Example

nim r testament/testament.nim r tests/errmsgs/undeclared_routime4.nim

Current Output

FAIL: tests/errmsgs/undeclared_routime4.nim c
Test "tests/errmsgs/undeclared_routime4.nim" in category "errmsgs"
Failure: reMsgsDiffer
Expected:
undeclared_routime4.nim(10, 10) Error: undeclared field: 'bar'


Gotten:
undeclared_routime4.nim(10, 10) Error: undeclared field: 'bar' for type undeclared_routime4.Foo [type declared in undeclared_routime4.nim(8, 6)]

Expected Output

works

Additional Information

1.5.1 01bca8c
nim r testament/testament.nim pcat errmsgs still works (that's what's tested in CI, but r instead of pcat is uesful during development allowing to test 1 specific test and should keep working)

#16698 was a good PR but it needs an adjustment to handle this correctly

#17861 also sheds some explanation on this: the test files started with u, not t, so were never run in CI, which probably explains why pcat works but not r; nevertheless, this is a (hopefully easily fixable) regression that is probably specific to only those files tests/errmsgs/[^t]*.nim

[timotheecour]

=> #17862