unit test coverage: fix missing coverage

[martinkunkel2]

binary-path option of grcov needs to be set to full target/debug folder to include unit test binaries.

This fixes #9597

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/cksum/b2sum is no longer failing!

[martinkunkel2]

compared results:

on main: 41164 of 46764 lines covered
with this pr: 46632 of 52979 lines covered

see https://app.codecov.io/gh/uutils/coreutils/tree/martinkunkel2%2Fcoreutils%3Acoverage-for-unit-tests/src

and example lines.rs: https://app.codecov.io/gh/uutils/coreutils/blob/martinkunkel2%2Fcoreutils%3Acoverage-for-unit-tests/src%2Fuucore%2Fsrc%2Flib%2Ffeatures%2Flines.rs

[ChrisDryden]

Is it accurate to have the unit test lines counted as lines to track? https://app.codecov.io/gh/uutils/coreutils/blob/main/src%2Fuucore%2Fsrc%2Flib%2Ffeatures%2Flines.rs
vs
https://app.codecov.io/gh/uutils/coreutils/blob/martinkunkel2%2Fcoreutils%3Acoverage-for-unit-tests/src%2Fuucore%2Fsrc%2Flib%2Ffeatures%2Flines.rs

[martinkunkel2]

valid remark. I'll investigate

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[martinkunkel2]

@ChrisDryden : I could apply a filter that removes the test code from coverage, see 7067251
Fix is similar to what is proposed in mozilla/grcov#728

Latest test run: https://app.codecov.io/gh/uutils/coreutils/blob/martinkunkel2%2Fcoreutils%3Acoverage-for-unit-tests/src%2Fuucore%2Fsrc%2Flib%2Ffeatures%2Flines.rs

[martinkunkel2]

@sylvestre : this is ready for review.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[RenjiSann]

Looks good to me !
Thank you !