Check remove_after date format

app/models/concerns/ignorable_columns.rb

@@ -18,7 +18,7 @@ module IgnorableColumns
     #
     # Indicate the earliest date and release we can stop ignoring the column with +remove_after+ (a date string) and +remove_with+ (a release)
     def ignore_columns(*columns, remove_after:, remove_with:)
-      raise ArgumentError, 'Please indicate when we can stop ignoring columns with remove_after (date string), example: ignore_columns(:name, remove_after: \'2019-12-01\', remove_with: \'12.6\')' unless remove_after
+      raise ArgumentError, 'Please indicate when we can stop ignoring columns with remove_after (date string YYYY-MM-DD), example: ignore_columns(:name, remove_after: \'2019-12-01\', remove_with: \'12.6\')' unless remove_after =~ Gitlab::Regex.utc_date_regex
       raise ArgumentError, 'Please indicate in which release we can stop ignoring columns with remove_with, example: ignore_columns(:name, remove_after: \'2019-12-01\', remove_with: \'12.6\')' unless remove_with
 
       self.ignored_columns += columns.flatten # rubocop:disable Cop/IgnoredColumns

spec/models/concerns/ignorable_columns_spec.rb

@@ -27,6 +27,10 @@ describe IgnorableColumns do
     expect { subject.ignore_columns(:name, remove_after: nil, remove_with: 12.6) }.to raise_error(ArgumentError, /Please indicate/)
   end
 
+  it 'requires remove_after attribute to be set' do
+    expect { subject.ignore_columns(:name, remove_after: "not a date", remove_with: 12.6) }.to raise_error(ArgumentError, /Please indicate/)
+  end
+
   it 'requires remove_with attribute to be set' do
     expect { subject.ignore_columns(:name, remove_after: '2019-12-01', remove_with: nil) }.to raise_error(ArgumentError, /Please indicate/)
   end