docs build failed in `google-shopping-merchant-accounts`

[parthea]

See https://github.com/googleapis/googleapis/blob/9516e70a70d6f7e0cd000ddd370d73656da09b96/google/shopping/merchant/accounts/v1beta/emailpreferences.proto#L38-L41 where there is an asterisk character which is not surrounded by backticks or escaped.

This caused the docs build to fail with

sphinx.errors.SphinxWarning: /home/runner/work/google-cloud-python/google-cloud-python/packages/google-shopping-merchant-accounts/google/shopping/merchant_accounts_v1beta/services/email_preferences_service/async_client.py:docstring of google.shopping.merchant_accounts_v1beta.services.email_preferences_service.async_client.EmailPreferencesServiceAsyncClient.get_email_preferences:4:Inline emphasis start-string without end-string.

Instead of

  // Returns the email preferences for a Merchant Center account user.
  //
  // Use the name=accounts/*/users/me/emailPreferences alias to get preferences
  // for the authenticated user.

It should be

  // Returns the email preferences for a Merchant Center account user.
  //
  // Use the name=`accounts/*/users/me/emailPreferences` alias to get preferences
  // for the authenticated user.

See https://github.com/googleapis/google-cloud-python/actions/runs/9422535846/job/25959043051?pr=12786

We should add a check upstream for unsupported formatting in proto comments