Update suffix concatenation to handle nil values - form 10-7959f-1

[michaelclement]

Summary

This PR updates the JSON erb mapping for form 10-7959f-1 so that the concatenation of suffix to lastname works even when suffix isn't provided. Previously, we would get an type error
no implicit conversion of nil into String. By switching to use join() rather than +, nil values are handled gracefully.

• Fixes string concatenation for suffixes in JSON erb

Related issue(s)

• 92068 Update PDF layout - form 10-7959f-1 #18298

Testing done

• New code is covered by unit tests
• Describe what the old behavior was prior to the change
• Describe the steps required to verify your changes are working as expected. Exclusively stating 'Specs run' is NOT acceptable as appropriate testing
• If this work is behind a flipper:
  • Tests need to be written for both the flipper on and flipper off scenarios. Docs.
  • What is the testing plan for rolling out the feature?

Screenshots

	Nil suffix	Suffix present
PDF

What areas of the site does it impact?

This form only

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

Requested Feedback

NA