fix: convert refreshed_at to UTC before updating

[kangmingtay]

What kind of change does this PR introduce?

• Fixes an issue with session inactivity timeout where the session's refreshed_at time is being saved without the timezone since the underlying postgres type uses timestamp without time zone. This means that when the timestamp is later queried from the database, go assumes that the timestamp is in UTC (since there's no timezone information stored).
• Decided not to add a migration to update the database type since this could be an expensive operation for users with large auth.sessions tables.

[coveralls]

Pull Request Test Coverage Report for Build 12800829185

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 65.445%

---

Totals
Change from base Build 12786188298:	0.01%
Covered Lines:	9818
Relevant Lines:	15002

---

💛 - Coveralls