PROBLEM: The builtin python3 provider cannot auto-detect python3.12
when g:python3_host_prog is not set. As a result, when python3 on $PATH
is currently python 3.12, neovim will fail to load python3 provider
and result in `has("python3") == 0`, e.g.,
"Failed to load python3 host. You can try to see what happened by ..."
ROOT CAUSE: the `system()` call from `provider#pythonx#DetectByModule`
does not ignore python warnings, and `pkgutil.get_loader` will print
a warning message in the very first line:
```
<string>:1: DeprecationWarning: 'pkgutil.get_loader' is deprecated and
slated for removal in Python 3.14; use importlib.util.find_spec() instead
```
SOLUTION:
- Use `importlib.util.find_spec` instead (python >= 3.4)
- Use `-W ignore` option to prevent any potential warning messages
(cherry picked from commit 3da511f1d0)