[misc] Fix manylinux2014 warning not printing (#7270)

Issue: #

### Brief Summary

Author: feisuzhu

python/taichi/__init__.py

@@ -2,6 +2,7 @@
 
 from taichi._funcs import *
 from taichi._lib import core as _ti_core
+from taichi._lib.utils import warn_restricted_version
 from taichi._logging import *
 from taichi._snode import *
 from taichi.lang import *  # pylint: disable=W0622 # TODO(archibate): It's `taichi.lang.core` overriding `taichi.core`
@@ -93,3 +94,6 @@ def __getattr__(attr):
 
 del sys
 del _ti_core
+
+warn_restricted_version()
+del warn_restricted_version

python/taichi/_lib/utils.py

@@ -2,6 +2,7 @@
 import platform
 import re
 import sys
+import warnings
 
 from colorama import Fore, Style
 
@@ -202,7 +203,9 @@ def try_get_loaded_libc_version():
 
 def try_get_pip_version():
     try:
-        import pip  # pylint: disable=import-outside-toplevel
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore")
+            import pip  # pylint: disable=import-outside-toplevel
         return tuple([int(v) for v in pip.__version__.split('.')])
     except ImportError:
         return None
@@ -244,6 +247,3 @@ def warn_restricted_version():
                 )
         except Exception:
             pass
-
-
-warn_restricted_version()