style(ui): remove hover backgrounds from icon actions

src/features/vcs/DiffEditor.module.css

@@ -151,7 +151,7 @@
 }
 .host :global(.cm-merge-revert button:hover) {
   color: var(--fg-strong);
-  background: var(--bg-hover);
+  background: transparent;
 }
 .select {
   height: var(--h-control-small);
@@ -277,7 +277,7 @@
 }
 .host :global(.cm-diffDivider button.cm-diffArrow:hover) {
   color: var(--fg-strong);
-  background: var(--bg-hover);
+  background: transparent;
 }
 /* Where the other pane has lines this one lacks. */
 .host :global(.cm-diffGap-inserted) {