Fix merge request thread’s icon buttons color

Currently the buttons look disabled because of the
very light gray icons. This aligns the icon’s color
with the Pajamas button design specs
(https://design.gitlab.com/components/button/).

app/assets/stylesheets/pages/note_form.scss

@@ -281,7 +281,7 @@ table {
     display: table;
 
     svg {
-      fill: $gray-darkest;
+      fill: $gray-700;
     }
 
     .btn-group {

app/assets/stylesheets/pages/notes.scss

@@ -855,7 +855,7 @@ $note-form-margin-left: 72px;
     line-height: $gl-line-height;
 
     svg {
-      fill: $gray-darkest;
+      fill: $gray-700;
     }
 
     &.discussion-create-issue-btn {
@@ -893,7 +893,7 @@ $note-form-margin-left: 72px;
 
   .line-resolve-btn {
     margin-right: 5px;
-    color: $gray-darkest;
+    color: $gray-700;
 
     svg {
       vertical-align: middle;

changelogs/unreleased/pedroms-fix-mr-threads-icon-button-color.yml

+---
+title: Fix merge request thread’s icon buttons color
+merge_request: 28465
+author:
+type: other