fix(rails): set dummy rails app before calling initializers

[solnic]

I noticed a flaky failure in the new DC specs and it turned out to be an issue with our Rails dummy app init process - this should fix it.

With the fix this and most likely other specs will not be flaky:

Failures:

  1) Sentry::Rails data collection adds Rails filter parameters to URL query parameter data collection
     Failure/Error:
       expect(Sentry.configuration.data_collection.url_query_params.terms).to include(
         "password",
         "custom_secret"
       )

       expected [] to include "password" and "custom_secret"
     # ./spec/sentry/rails_spec.rb:117:in `block (3 levels) in <top (required)>'

Finished in 37.38 seconds (files took 1.18 seconds to load)
290 examples, 1 failure, 34 pending

Failed examples:

rspec ./spec/sentry/rails_spec.rb:116 # Sentry::Rails data collection adds Rails filter parameters to URL query parameter data collection

Randomized with seed 19348

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