Fixed spacing issues in issue sidebar

When we removed the nicescroll plugin from issues it causes some spacing issues that were added to make nicescroll play nice. This fixes that by fixing some of the padding that was causing the scroll area to be incorrect & the collapsed sidebar to have overflow issues

Closes #32357

app/assets/stylesheets/pages/issuable.scss

@@ -195,7 +195,7 @@
   right: 0;
   transition: width .3s;
   background: $gray-light;
-  padding: 10px 20px;
+  padding: 0 20px;
   z-index: 200;
   overflow: hidden;
@@ -219,6 +219,10 @@
       }
     }
+    .issuable-sidebar-header {
+      padding-top: 10px;
+    }
+
     .assign-yourself .btn-link {
       padding-left: 0;
     }
@@ -272,11 +276,10 @@
     }
     width: $gutter_collapsed_width;
-    padding-top: 0;
+    padding: 0;
     .block {
       width: $gutter_collapsed_width - 2px;
-      margin-left: -19px;
       padding: 15px 0 0;
       border-bottom: none;
       overflow: hidden;