Fix ArgumentError when Warning.process is used again

What does this MR do and why?

This MR fixes an ArgumentError raised after Warning.process is used twice.

Consider this:

require 'warning'

Warning.process(/foo/) { :raise }
Warning.process(/bar/) { :raise }
# => ArgumentError (comparison of Regexp with Regexp failed)

The first argument of Warning.process must be a path and actions can be passed as a Hash:

require 'warning'

Warning.process('', /foo/ => :raise)
Warning.process('', /bar/ => :raise)
warn("foo") # => RuntimeError (foo)
warn("bar") # => RuntimeError (bar)

There's an upstream GitHub issue that discusses this problem: https://github.com/jeremyevans/ruby-warning/issues/17 (closed) and the fix https://github.com/jeremyevans/ruby-warning/pull/19 (merged).

How to set up and validate locally

On master do:

• bundle exec rails console
• Warning.process('') { :raise }
• 💥 ArgumentError: comparison of Regexp with String failed

On pl-fix-log-deprecations-initializer do:

• bundle exec rails console
• Warning.process('') { :raise }
• Verify via warn 'anything' to raise RuntimeError: anything ✅

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.