Fix Lint/RedundantSafeNavigation when using to_s

[lucthev]

A Rails project I work on has code vaguely similar

maybe_time&.to_s(:iso8601) || '(Unknown)'

The changes made in #11890 cause Lint/RedundantSafeNavigation to suggest removing the safe navigation from the above code. This has been discussed before in #8867, but to summarize, removing the safe navigation is undesirable because:

• nil.to_s(:iso8601) would raise an ArgumentError

• Even in the more general case, when there are no extra arguments to to_s, removing the safe navigation changes the semantics:

  nil&.to_s || '(Unknown)' # => '(Unknown)'
  nil.to_s || '(Unknown)' # => ''

This PR reverts #11890 and adds a test to prevent regressions.

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[koic]

Oops! I made the mistake. Thank you for catching up!

[john-h-k]

Could we get a minor release for this?

[bbatsov]

@john-h-k I'll likely cut one before the end of the week. There are a few other bug-fix PRs I'd like to merge first.