Merge branch 'fix-input-placeholder-color' into 'master'

Fix input placeholder text color

Closes #47645

See merge request gitlab-org/gitlab-ce!19633

app/assets/stylesheets/framework/forms.scss

@@ -170,7 +170,7 @@ label {
 }
 
 .form-control::-webkit-input-placeholder {
-  color: $gl-text-color-secondary;
+  color: $placeholder-text-color;
 }
 
 .input-group {