fix(src): use `errors.Is(err, fs.ErrNotExist)`

[laushunyu]

I implemented fs.FS. When the file does not exist, xerrors.Wrap(fs.ErrNotExist, "") will be returned. However, os.IsNotExist cannot handle this situation. I found the following comment:

// IsNotExist returns a boolean indicating whether the error is known to
// report that a file or directory does not exist. It is satisfied by
// ErrNotExist as well as some syscall errors.
//
// This function predates errors.Is. It only supports errors returned by
// the os package. New code should use errors.Is(err, fs.ErrNotExist).

Therefore, we should use errors.Is(err, fs.ErrNotExist) instead.

[CLAassistant]

All committers have signed the CLA.

[ldez]

@laushunyu you have to use an email related to your GitHub account to create your commit. After that you will have to sign the CLA.

[laushunyu]

@laushunyu you have to use an email related to your GitHub account to create your commit. After that you will have to sign the CLA.

email corrected😇.