The PR fixes a test flakiness issue in test_mv_backlog related to reading metrics.
The first commit fixes a more general issue in the ScyllaMetrics helper class where it doesn't return the value of all matching lines when a specific shard is requested, but it breaks after the first match.
The second commit fixes a test issue where it expects exactly one write to be throttled, not taking into account other internal writes that may be executed during this time.
Fixes https://github.com/scylladb/scylladb/issues/23139
backport to improve CI stability - test only change
- (cherry picked from commit 5c28cffdb4)
- (cherry picked from commit 276a09ac6e)
Parent PR: #25279Closesscylladb/scylladb#25474
* github.com:scylladb/scylladb:
test: test_mv_backlog: fix to consider internal writes
test/pylib/rest_client: fix ScyllaMetrics filtering
39a85df231