[9.18] fix: test: Increase wait_for_log timeout in kasp shell test

When running with TSAN in CI, the test ocassionally fails on:

exceeded time limit waiting for literal 'keymgr: purgekeys.kasp done' in ns4/named.run

The line is actually present in the logs, but it take slightly longer
than 3 seconds to appear. Increase the wait_for_log timeout of the kasp test to 10
seconds to avoid such issues.

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Example of failure: https://gitlab.isc.org/isc-projects/bind9/-/jobs/6176192

Merge branch 'nicki/kasp-shell-test-increase-log-timeout' into 'bind-9.18'

See merge request isc-projects/bind9!10976