🥅 Workaround https://bugs.ruby-lang.org/issues/20956

This looks like a bug in prism:
```
$ rbenv shell 3.4.0-rc1
$ ruby -e 'pp ([["foo"]] in [/\Afoo\b/i | [/\Afoo\z/i, *]])'
false
$ ruby --parser=parse.y -e 'pp ([["foo"]] in [/\Afoo\b/i | [/\Afoo\z/i, *]])'
true
```

lib/net/imap.rb

@@ -3248,6 +3248,10 @@ def search_args(keys, charset_arg = nil, return: nil, charset: nil)
         esearch = false
       in [_, Array[RETURN_WHOLE, _, *] | RETURN_START]
         raise ArgumentError, "conflicting return options"
+      in [_, Array[RETURN_WHOLE, _, *]] # workaround for https://bugs.ruby-lang.org/issues/20956
+        raise ArgumentError, "conflicting return options"
+      in [_, RETURN_START]              # workaround for https://bugs.ruby-lang.org/issues/20956
+        raise ArgumentError, "conflicting return options"
       in [return_opts, keys]
         return_opts = convert_return_opts(return_opts)
         esearch = true