chg: test: Match algorithms when checking signatures

In the ksr system test, the 'test_ksr_twotone' case may fail if there are two keys with the same keytag (but different algorithms), because one key is expected to be signing and the other is not.

Switch to regular expression matching and include the algorithm in the search string.

Closes #5017

Merge branch '5017-unexpected-match-ksr-twotone-again' into 'main'

See merge request isc-projects/bind9!9701