Add model validation to Design to limit filename

https://gitlab.com/gitlab-org/gitlab/-/issues/209025

app/models/design_management/design.rb

@@ -22,7 +22,7 @@ module DesignManagement
 
     validates :project, :filename, presence: true
     validates :issue, presence: true, unless: :importing?
-    validates :filename, uniqueness: { scope: :issue_id }
+    validates :filename, uniqueness: { scope: :issue_id }, length: { maximum: 255 }
     validate :validate_file_is_image
 
     alias_attribute :title, :filename

spec/models/design_management/design_spec.rb

@@ -27,6 +27,7 @@ describe DesignManagement::Design do
     it { is_expected.to validate_presence_of(:project) }
     it { is_expected.to validate_presence_of(:issue) }
     it { is_expected.to validate_presence_of(:filename) }
+    it { is_expected.to validate_length_of(:filename).is_at_most(255) }
     it { is_expected.to validate_uniqueness_of(:filename).scoped_to(:issue_id) }
 
     it "validates that the extension is an image" do