fix(test_list_all_available_nemesis): fix number of disrupt methods

[mikliapko]

Fix expected number of disrupt methods in test_list_all_available_nemesis test.

Testing

• https://jenkins.scylladb.com/job/sct-github-PRs-scan/job/scylla-cluster-tests/job/PR-7753/workflow-stage/

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)