Fix UserInputError GraphQL errors

[jeffm2001]

Description

If you try to use the bulk reassign button in the admin message review screen, you get a GraphQL UserInputError because newTexterUserId is an int instead of the expected string.

Checklist:

• I have manually tested my changes on desktop and mobile
• The test suite passes locally with my changes
• If my change is a UI change, I have attached a screenshot to the description section of this pull request
• My change is 300 lines of code or less, or has a documented reason in the description why it’s longer
• I have made any necessary changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• My PR is labeled [WIP] if it is in progress

[jeffm2001]

Found some additional UserInputError issues on the Sweep Conversations page and on the Message Review page when filtering by error code

[mau11]

thanks so much Jeff for fixing this! We've been seeing a lot of type errors since updating to Node 20.

Although this is working, I noticed this error in the logs: backend error TypeError: Cannot read properties of null (reading 'toString') coming from src/server/api/conversations.js:498, can you add a null check? Aside from that, looks great!

          assignmentId: assignmentId?.toString()

[jeffm2001]

Yep, makes sense!