[3.13] gh-143135: Fix sys.flags.inspect when PYTHONINSPECT=0 (GH-143136) (GH-143168)

(cherry picked from commit 3509fa5)

Author: StanFromIreland

Misc/NEWS.d/next/Core and Builtins/2025-12-24-11-39-59.gh-issue-143135.3d5ovx.rst

@@ -0,0 +1,2 @@
+Set :data:`sys.flags.inspect` to ``1`` when :envvar:`PYTHONINSPECT` is ``0``.
+Previously, it was set to ``0`` in this case.

Python/initconfig.c

@@ -1576,7 +1576,9 @@ config_read_env_vars(PyConfig *config)
     _Py_get_env_flag(use_env, &config->parser_debug, "PYTHONDEBUG");
     _Py_get_env_flag(use_env, &config->verbose, "PYTHONVERBOSE");
     _Py_get_env_flag(use_env, &config->optimization_level, "PYTHONOPTIMIZE");
-    _Py_get_env_flag(use_env, &config->inspect, "PYTHONINSPECT");
+    if (!config->inspect && _Py_GetEnv(use_env, "PYTHONINSPECT")) {
+        config->inspect = 1;
+    }
 
     int dont_write_bytecode = 0;
     _Py_get_env_flag(use_env, &dont_write_bytecode, "PYTHONDONTWRITEBYTECODE");