Exclude .repo folders by default (#34431)

These are used by [Google's `repo`
tool](https://android.googlesource.com/tools/repo) used for Android for
managing hundreds of git subprojects.

Originally reported in:
- https://github.com/zed-industries/zed/issues/34302

Release Notes:

- Add Google Repo `.repo` folders to default `file_scan_exclusions`

assets/settings/default.json

@@ -1135,6 +1135,7 @@
     "**/.svn",
     "**/.hg",
     "**/.jj",
+    "**/.repo",
     "**/CVS",
     "**/.DS_Store",
     "**/Thumbs.db",