BUGFIX: null year-month for pharmacy in PMPM

[sarah-tuva]

Describe your changes

Resolves #452.

• removed incorrect date cast causing nulls for pharmacy claims
• refactored formatting to match style guide

How has this been tested?

Ran dbt build and validated output. Pharmacy claims have year_month populated now.

Reviewer focus

Please summarize the specific items you’d like the reviewer(s) to look into.

Checklist before requesting a review

• [x] I have added at least one Github label to this PR (bug, enhancement, breaking change,...)
• [x] My code follows style guidelines
• [ ] (New models) YAML files are categorized by sub folder and models listed in alphabetical order
• [ ] (New models) I have added a config to each new model to enable it for claims and/or clinical data
• [ ] (New models) I have added the variable tuva_last_run to the final output
• [ ] (Optional) I have recorded a Loom to explain this PR

Package release checklist

• [ ] I have updated dbt docs
• [ ] I have updated the version number in the dbt_project.yml

(Optional) Gif of how this PR makes you feel

Loom link