Validate hex colors when creating/editing labels (go-gitea#34623) (go-gitea#34630)

Backport go-gitea#34623

---------

Co-authored-by: Kemal Zebari <[email protected]>

Author: wxiaoguang

templates/repo/issue/labels/label_edit_modal.tmpl

@@ -50,7 +50,7 @@
 			<div class="field">
 				<label for="color">{{ctx.Locale.Tr "repo.issues.label_color"}}</label>
 				<div class="column js-color-picker-input">
-					<input name="color" value="#70c24a" placeholder="#c320f6" required maxlength="7">
+					<input name="color" value="#70c24a" placeholder="#c320f6" required pattern="^#?([\dA-Fa-f]{3}|[\dA-Fa-f]{6})$" maxlength="7">
 					{{template "repo/issue/label_precolors"}}
 				</div>
 			</div>