Bug 1903995 - [devtools] Disable selection on the line number gutters…

… r=devtools-reviewers,nchevobbe

Differential Revision: https://phabricator.services.mozilla.com/D215067

UltraBlame original commit: 52879d7076e96efee17fc56f9f8feafc2ddb79ae

devtools/client/shared/sourceeditor/codemirror/mozilla.css

@@ -2221,6 +2221,26 @@ editor
 .
 cm
 -
+gutter
+.
+cm
+-
+lineNumbers
+{
+user
+-
+select
+:
+none
+;
+}
+.
+cm
+-
+editor
+.
+cm
+-
 foldPlaceholder
 {
 font