testsuite: make find_so regex less general

Closes #24759

Background. In MR !12372 we began tracking shared object files and
directories sizes for dependencies. However, this broke  release builds
because release builds alter the filenames swapping "in-place" for a
hash. This was not considered in the MR and thus broke release
pipelines. Furthermore, the rts_so test was found to be wildly varying
and was therefore disabled in !12561.

This commit fixes both of these issues:

- fix the rts_so test by making the regex less general, now the rts_so
test and all other foo.so tests must match
"libHS<some-lib>-<version>-<hash|'in-place>-<ghc>". This prevents the
rts_so test from accidentally matching different rts variants such as
rts_threaded, which was the cause of the wild swings after !12372.

- add logic to match either a hash or the string in-place. This should
make the find_so function build agnostic.