Fix a false positive for Rails/DynamicFindBy

[koic]

This PR fixes a false positive for Rails/DynamicFindBy when any of the arguments are splat argument.

% cat example.rb
find_by_scan(*args)

% bundle exec rubocop -a example.rb
(snip)

Inspecting 1 file
E

Offenses:

example.rb:1:1: C: [Corrected] Rails/DynamicFindBy: Use find_by instead
of dynamic find_by_scan.
find_by_scan(*args)
^^^^^^^^^^^^^^^^^^^
example.rb:1:15: E: Lint/Syntax: unexpected token tSTAR
(Using Ruby 2.7 parser; configure using TargetRubyVersion parameter,
under AllCops)
find_by(scan: *args)
              ^

1 file inspected, 2 offenses detected, 1 offense corrected

% cat example.rb
find_by(scan: *args)

% ruby -c example.rb
example.rb:1: syntax error, unexpected *
find_by(scan: *args)

---

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
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