[9.20] chg: test: Don't check the EDE extra text in dnssec tests

While the extra text field in EDE can be useful debug information, it
doesn't need to be checked in the tests. In some cases, differences in
caching could lead to slightly different messages which would trigger a
false positive test result. Omit these checks, as they're no longer
checked for anyway in 9.21+ where the test has been rewritten to python.

Closes #5512

Merge branch '5512-dont-check-ede-text-in-tests' into 'bind-9.20'

See merge request isc-projects/bind9!11026