Summary:
Fix style issues in `src/backend/tcop/postgres.c` as reported by arc lint.
Fixes to `likely_bad_capitalization_in_errmsg` warnings are excluded from this revision as that would constitute a user facing change.
Jira: DB-14373

Test Plan: Jenkins: compile only

Reviewers: telgersma

Reviewed By: telgersma

Subscribers: telgersma, yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D40485