Correct _FREE_THREADED_BUILD detection for Py_GIL_DISABLED

`sysconfig.get_config_var("Py_GIL_DISABLED")` may be defined as 0 on
non-free-threaded builds. The previous check used `is not None`, which
incorrectly treated `Py_GIL_DISABLED=0` as a free-threaded build.

Signed-off-by: Yongtao Huang <yongtaoh2022@gmail.com>

Author: hyongtao-code

Lib/profiling/sampling/sample.py

@@ -41,7 +41,7 @@ def _pause_threads(unwinder, blocking):
 except ImportError:
     LiveStatsCollector = None
 
-_FREE_THREADED_BUILD = sysconfig.get_config_var("Py_GIL_DISABLED") is not None
+_FREE_THREADED_BUILD = bool(sysconfig.get_config_var("Py_GIL_DISABLED"))
 # Minimum number of samples required before showing the TUI
 # If fewer samples are collected, we skip the TUI and just print a message
 MIN_SAMPLES_FOR_TUI = 200