BugFix: Use first-of-type for buttongroup selector (#5343)

* BugFix: Use first-of-type for buttongroup selector

* test(vrt): update snapshots

* Create big-jokes-jog.md

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Co-authored-by: jonrohan <jonrohan@users.noreply.github.com>

Author: jonrohan

.changeset/big-jokes-jog.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": patch
+---
+
+BugFix: Fix issue in ButtonGroup Overlay screenshots by updating the selector to use `:is(button, a)` and `:first-of-type` and `:last-of-type` pseudo-classes.