[Fix #6603] - Testing RescueEnsureAlignment

[jaredbeck]

Add a test to demonstrate the correct styles of a begin-rescue as the
RHS of an assignment.

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Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[jaredbeck]

I think we also need a similar example when the begin is on the same line as the assignment op.

Example added.

[jaredbeck]

I think this is ready to merge. The fact that appveyor failed ("Could not find gem 'safe_yaml x86-mingw32'") seems unrelated to my changes.

[bbatsov]

Thanks!