Default granularity bug fix: handle time dimensions with the same name

[courtneyholcomb]

Description

Found another bug in SetDefaultGranularityRule. If there are multiple agg_time_dimensions with the same name across semantic models, and they have different granularities, we'll only check one. Fixed here!

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have signed the CLA
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [ ] I have run changie new to create a changelog entry