Fix syntax error

2 jobs for dm-add-mirror-queries in 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #2250707
rspec

00:00:25

failed #2250708
rubocop

00:00:23

 
Name Stage Failure
failed
rubocop Test
lib/gitlab_monitor/database/row_count.rb:10:32: C: Style/MutableConstant: Freeze mutable objects assigned to constants.
WHERE_MIRROR_ENABLED = <<~SQL
^^^^^^
lib/gitlab_monitor/database/row_count.rb:16:24: C: Style/MutableConstant: Freeze mutable objects assigned to constants.
MIRROR_QUERY = { ...
^

26 files inspected, 2 offenses detected
ERROR: Job failed: exit code 1