Fix T51444: Unit tests don't run on Windows

Referenced by issue #51444, Python scripts executed from commandline don't have __main__ module's dict as their globals on Windows

source/blender/python/intern/bpy_interface.c

@@ -480,11 +480,20 @@ static bool python_script_exec(
 			 * object, but as written in the Python/C API Ref Manual, chapter 2,
 			 * 'FILE structs for different C libraries can be different and
 			 * incompatible'.
-			 * So now we load the script file data to a buffer */
+			 * So now we load the script file data to a buffer.
+			 *
+			 * Note on use of 'globals()', it's important not copy the dictionary because
+			 * tools may inspect 'sys.modules["__main__"]' for variables defined in the code
+			 * where using a copy of 'globals()' causes code execution
+			 * to leave the main namespace untouched. see: T51444
+			 *
+			 * This leaves us with the problem of variables being included,
+			 * currently this is worked around using 'dict.__del__' it's ugly but works.
+			 */
 			{
 				const char *pystring =
-				        "ns = globals().copy()\n"
-				        "with open(__file__, 'rb') as f: exec(compile(f.read(), __file__, 'exec'), ns)";
+				        "with open(__file__, 'rb') as f:"
+				        "exec(compile(f.read(), __file__, 'exec'), globals().__delitem__('f') or globals())";
 
 				fclose(fp);