Drop `milestone_id` Column From Vulnerabilities

What does this MR do and why?

milestone_id is an ignored column (source)

This MR drops the column for step 2 of the 3-MR drop column process

Check for indexes or constraints

Using the command \d+ vulnerabilities on postgres.ai indicates there ARE indexes and constraints

index	fk constraint

migration output

bundle exec rails db:migrate output

~/gitlab-development-kit/gitlab$ bundle exec rails db:migrate 
main: == [advisory_lock_connection] object_id: 182760, pg_backend_pid: 254337
main: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: migrating =======
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- remove_column(:vulnerabilities, :milestone_id)
main:    -> 0.0011s
main: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: migrated (0.0082s) 

main: == [advisory_lock_connection] object_id: 182760, pg_backend_pid: 254337
ci: == [advisory_lock_connection] object_id: 183000, pg_backend_pid: 254339
ci: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: migrating =======
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- remove_column(:vulnerabilities, :milestone_id)
ci:    -> 0.0009s
ci: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: migrated (0.0081s) 

ci: == [advisory_lock_connection] object_id: 183000, pg_backend_pid: 254339

bundle exec rails db:rollback:main output

~/gitlab-development-kit/gitlab$ bundle exec rails db:rollback:main
main: == [advisory_lock_connection] object_id: 182500, pg_backend_pid: 258005
main: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: reverting =======
main: -- column_exists?(:vulnerabilities, :milestone_id)
main:    -> 0.0152s
main: -- add_column(:vulnerabilities, :milestone_id, :bigint)
main:    -> 0.0011s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0007s
main: -- index_exists?(:vulnerabilities, :milestone_id, {:algorithm=>:concurrently})
main:    -> 0.0081s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- add_index(:vulnerabilities, :milestone_id, {:algorithm=>:concurrently})
main:    -> 0.0014s
main: -- execute("RESET statement_timeout")
main:    -> 0.0003s
main: -- index_name(:vulnerabilities, :milestone_id)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- execute("ALTER TABLE vulnerabilities ADD CONSTRAINT fk_131d289c65 FOREIGN KEY (milestone_id) REFERENCES milestones (id) ON DELETE SET NULL NOT VALID;")
main:    -> 0.0145s
main: -- execute("ALTER TABLE vulnerabilities VALIDATE CONSTRAINT fk_131d289c65;")
main:    -> 0.0035s
main: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: reverted (0.0790s) 

main: == [advisory_lock_connection] object_id: 182500, pg_backend_pid: 258005

bundle exec rails db:rollback:ci output

~/gitlab-development-kit/gitlab$ bundle exec rails db:rollback:ci
ci: == [advisory_lock_connection] object_id: 182300, pg_backend_pid: 258451
ci: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: reverting =======
ci: -- column_exists?(:vulnerabilities, :milestone_id)
ci:    -> 0.0134s
ci: -- add_column(:vulnerabilities, :milestone_id, :bigint)
ci:    -> 0.0008s
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- view_exists?(:postgres_partitions)
ci:    -> 0.0006s
ci: -- index_exists?(:vulnerabilities, :milestone_id, {:algorithm=>:concurrently})
ci:    -> 0.0082s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0001s
ci: -- add_index(:vulnerabilities, :milestone_id, {:algorithm=>:concurrently})
ci:    -> 0.0008s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0001s
ci: -- index_name(:vulnerabilities, :milestone_id)
ci:    -> 0.0000s
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- execute("ALTER TABLE vulnerabilities ADD CONSTRAINT fk_131d289c65 FOREIGN KEY (milestone_id) REFERENCES milestones (id) ON DELETE SET NULL NOT VALID;")
ci:    -> 0.0197s
ci: -- execute("ALTER TABLE vulnerabilities VALIDATE CONSTRAINT fk_131d289c65;")
ci:    -> 0.0045s
ci: == 20240102065444 RemoveMilestoneIdColumnFromVulnerabilities: reverted (0.0781s) 

ci: == [advisory_lock_connection] object_id: 182300, pg_backend_pid: 258451

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #268154 (closed)