[9.20] chg: test: Add utility module to import correct version of hypothesis

On FIPS-enabled platforms, we need to ensure a minimal version of
hypothesis which no longer uses MD5. This doesn't need to be enforced
for other platforms.

Move the import magic to a utility module to avoid copy-pasting the
boilerplate code around.

Backport of MR !10442

Merge branch 'backport-nicki/pytest-import-hypothesis-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10507