gh-119132: Remove "experimental" tag from the CPython free-threading build

Author: corona10

Lib/platform.py

@@ -1144,7 +1144,7 @@ def _sys_version(sys_version=None):
         # CPython
         cpython_sys_version_parser = re.compile(
             r'([\w.+]+)\s*'  # "version<space>"
-            r'(?:experimental free-threading build\s+)?' # "free-threading-build<space>"
+            r'(?:free-threading build\s+)?' # "free-threading-build<space>"
             r'\(#?([^,]+)'  # "(#buildno"
             r'(?:,\s*([\w ]*)'  # ", builddate"
             r'(?:,\s*([\w :]*))?)?\)\s*'  # ", buildtime)<space>"

Python/getversion.c

@@ -15,7 +15,7 @@ void _Py_InitVersion(void)
     }
     initialized = 1;
 #ifdef Py_GIL_DISABLED
-    const char *buildinfo_format = "%.80s experimental free-threading build (%.80s) %.80s";
+    const char *buildinfo_format = "%.80s free-threading build (%.80s) %.80s";
 #else
     const char *buildinfo_format = "%.80s (%.80s) %.80s";
 #endif