[gdb/testsuite] Add another xfail case in gdb.python/py-record-btrace.exp

I ran into:
...
(gdb) PASS: gdb.python/py-record-btrace.exp: function call: \
  python print(c.prev)
python print(c == c.next.prev)^M
Traceback (most recent call last):^M
  File "<string>", line 1, in <module>^M
AttributeError: 'NoneType' object has no attribute 'prev'^M
Error while executing Python code.^M
(gdb) FAIL: gdb.python/py-record-btrace.exp: function call: \
  python print(c == c.next.prev)
...
due to having only 4 insn instead of 100:
...
python print(len(insn))^M
4^M
...

This could be caused by the same hw bug as we already have an xfail for, so
expand the xfail matching.

Tested on x86_64-linux.

PR testsuite/30185
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30185



Approved-By: Markus T. Metzger <markus.t.metzger@intel.com>