Validate hex colors when creating/editing labels (#34623)

Resolves #34618.

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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

options/locale/locale_en-US.ini

@@ -1433,7 +1433,6 @@ commitstatus.success = Success
 ext_issues = Access to External Issues
 ext_issues.desc = Link to an external issue tracker.
 
-projects = Projects
 projects.desc = Manage issues and pulls in projects.
 projects.description = Description (optional)
 projects.description_placeholder = Description
@@ -1653,6 +1652,7 @@ issues.save = Save
 issues.label_title = Name
 issues.label_description = Description
 issues.label_color = Color
+issues.label_color_invalid = Invalid color
 issues.label_exclusive = Exclusive
 issues.label_archive = Archive Label
 issues.label_archived_filter = Show archived labels