doc: fix inverted wrap direction on FileNotFoundFromSearchError

[ump45nose]

Overview:

Doc-comment-only correction on FileNotFoundFromSearchError (errors.go:36). The line reads // Wraps ConfigFileNotFoundError., which states the opposite of the actual relationship. It now reads // Wrapped by [ConfigFileNotFoundError]..

What problem does it solve?:

ConfigFileNotFoundError is the type that owns the Unwrap method, and it returns a FileNotFoundFromSearchError:

// Unwraps to FileNotFoundFromSearchError.
func (e ConfigFileNotFoundError) Unwrap() error {
	return FileNotFoundFromSearchError(e)
}

FileNotFoundFromSearchError has no Unwrap, and it is the only such method in errors.go. So ConfigFileNotFoundError is the outer error and FileNotFoundFromSearchError is the one being wrapped — the current comment inverts that, which is the kind of line a reader trusts when working out errors.Is/errors.As behaviour.

I confirmed it at runtime rather than only by reading, with a throwaway test in the package (since removed, not part of the diff):

outer=viper.ConfigFileNotFoundError unwraps to=viper.FileNotFoundFromSearchError

and errors.Unwrap(FileNotFoundFromSearchError{}) is nil.

Two notes on wording:

• Matched the bracketed-link form already used by the neighbouring ConfigFileNotFoundError comment ([FileNotFoundFromSearchError]) so godoc renders the cross-reference.
• This is a different line from open PR Fix "This is error wraps" doc typo on ConfigFileNotFoundError #2130, which fixes the This is error wraps grammar typo on line 19. No overlap in hunks.

Special notes for a reviewer:

No behavior change. Local checks:

• gofmt -l . — clean
• go vet ./... — clean
• go test -count=1 ./... — all 5 packages ok (uncached)