src/v/raft/tests: mark coordinated_compaction_test as flaky

[travisdowns]

Mark coordinated_compaction_test as flaky to unblock CI while the root cause is investigated.

Relates to CORE-15445

Backports Required

• none - not a bug fix

Release Notes

• none

[Copilot]

Pull request overview

This PR marks the coordinated_compaction_test as flaky in the Bazel build configuration to prevent it from blocking CI while the underlying issue (CORE-15445) is investigated.

Changes:

• Add flaky = True attribute to the coordinated_compaction_test build target

[travisdowns]

Test has been flaky forever.

[vbotbuildovich]

CI test results

test results on build#79879

test_class	test_method	test_arguments	test_kind	job_url	test_status	passed	reason	test_history
DataMigrationsApiTest	test_creating_and_listing_migrations	null	integration	https://buildkite.com/redpanda/redpanda/builds/79879#019c0cba-19a5-4cdc-9f51-fb198cbd4edf	FLAKY	10/11	Test PASSES after retries.No significant increase in flaky rate(baseline=0.0026, p0=1.0000, reject_threshold=0.0100. adj_baseline=0.1000, p1=0.3487, trust_threshold=0.5000)	https://redpanda.metabaseapp.com/dashboard/87-tests?tab=142-dt-individual-test-history&test_class=DataMigrationsApiTest&test_method=test_creating_and_listing_migrations
WriteCachingFailureInjectionE2ETest	test_crash_all	{"use_transactions": false}	integration	https://buildkite.com/redpanda/redpanda/builds/79879#019c0cb7-493b-4e3a-8380-3a7ce507c62a	FLAKY	9/11	Test PASSES after retries.No significant increase in flaky rate(baseline=0.0878, p0=0.6009, reject_threshold=0.0100. adj_baseline=0.2408, p1=0.2653, trust_threshold=0.5000)	https://redpanda.metabaseapp.com/dashboard/87-tests?tab=142-dt-individual-test-history&test_class=WriteCachingFailureInjectionE2ETest&test_method=test_crash_all