fix(tests): deflake useReplaysFromIssue test

[ryan953]

Summary

• Move shared mutable fixtures (location, organization, MOCK_GROUP) from describe scope into each individual test to prevent reference sharing across re-render cycles
• Split waitFor assertions: first wait for isFetching to settle to false, then assert eventView and fetchError synchronously outside waitFor to avoid deep-equal failures on transient intermediate states
• Remove it.isKnownFlake marker from the "should fetch a list of replay ids" test

Test plan

• CI passes on the previously flaky test
• All three tests in the suite continue to pass