[gdb/testsuite] Fix timeout in gdb.tui/wrap-line.exp

[gdb/testsuite] Fix timeout in gdb.tui/wrap-line.exp

When running test-case gdb.tui/wrap-line.exp on msys2-ucrt64, I run into a
timeout here:
...
	set test "startup prompt"
	gdb_test_multiple "" $test {
	    -re "^$gdb_prompt $" {
		pass "$test"
	    }
	}
...
due to running into "^[[6n(gdb) ".

Fix this by allowing this, similar to how this was fixed in default_gdb_start by
commit 7e1964f9c61 ("[gdb/testsuite] Set TERM to dumb by default").

Tested on x86_64-linux and msys2-ucrt64.

Approved-By: Tom Tromey <tom@tromey.com>