fix: partial character date formatting

[emilyjablonski]

This PR addresses #4292

• [x] Addresses the issue in full

Description

Allows you to enter partial dates in the partners listing form (i.e. 9/6/1994 instead of requiring 09/06/1994)

How Can This Be Tested/Reviewed?

Attempt to save a listing with a lottery date that has a partial month and day and ensure you don't receive an error.

Author Checklist:

• [x] Added QA notes to the issue with applicable URLs
• [x] Reviewed in a desktop view
• [x] Reviewed in a mobile view
• [x] Reviewed considering accessibility
• [x] Added tests covering the changes
• [ ] Made corresponding changes to the documentation
• [ ] Ran yarn generate:client and/or created a migration when required

Review Process:

• Read and understand the issue
• Ensure the author has added QA notes
• Review the code itself from a style point of view
• Pull the changes down locally and test that the acceptance criteria is met
• Either (1) explicitly ask a clarifying question, (2) request changes, or (3) approve the PR, even if there are very small remaining changes, if you don't need to re-review after the updates

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