Truncate ci_namespace_mirrors and ci_project_mirrors

We found a bug in processing sync events. After fixing it, we need to
repopulate tables. So, we are truncating them.

Changelog: other

db/post_migrate/20220111102314_truncate_ci_mirror_tables.rb

+# frozen_string_literal: true
+
+class TruncateCiMirrorTables < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  def up
+    execute('TRUNCATE TABLE ci_namespace_mirrors')
+    execute('TRUNCATE TABLE ci_project_mirrors')
+  end
+
+  def down
+    # noop
+  end
+end

db/schema_migrations/20220111102314

+69c20daf6a23346288e516df3e70120819d76dcb5fe2b1b51af416349311820b
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