fix(keymap): list the Git log's Show Diff in the VS Code preset (#3071)

#3065 bound vcs.log.changes.showDiff in the IntelliJ keymaps, and the VS Code
preset must name every IntelliJ action id (keymap.test.ts). VS Code has no Show
Diff key, so it gets none, like vcs.showDiff.

src/platform/keymaps/vscode-macos.ts

@@ -300,6 +300,7 @@ export const vscodeMacos: Record<string, string[]> = {
   "vcs.rollback": [],
   "vcs.addToVcs": [],
   "vcs.showDiff": [],
+  "vcs.log.changes.showDiff": [],
   "vcs.showDiffInNewWindow": [],
   "vcs.nextChange": ["Alt+F5"],
   "vcs.prevChange": ["Alt+Shift+F5"],