[gdb/testsuite] Two fixes in gdb.python/tui-window-disabled.exp

I ran test-case gdb.python/tui-window-disabled.exp on a configuration without
python support, and ran into:
...
PASS: $exp: cleanup_properly=True: initial restart: set pagination off
UNSUPPORTED: $exp: cleanup_properly=True: couldn't restart GDB
PASS: $exp: cleanup_properly=False: initial restart: set pagination off
UNSUPPORTED: $exp: cleanup_properly=False: couldn't restart GDB
...

After looking into the test-case, I realized that this is a consequence of
!allow_python_tests.

Handle this instead by requiring allow_python_tests, such that we get the usual
and more clear:
...
UNSUPPORTED: $exp: require failed: allow_python_tests
...

Also fix a return without value in clean_restart_and_setup, which if triggered
would cause:
...
ERROR: expected boolean value but got ""
...

Tested on x86_64-linux.

0 files changed, 0 insertions, 0 deletions