[v15] Bump github.com/jackc/pgx/v4 from 4.18.1 to 4.18.2

[codingllama]

Backport #39246 to branch/v15.

Manually updated / cherry picked from 4f36bba558:

go get github.com/jackc/pgx/v4@v4.18.2; go mod tidy;
git commit -am 'Bump github.com/jackc/pgx/v4 to v4.18.2'
git cherry-pick 4f36bba558

Changelog: Patched CVE-2024-27304 (Postgres driver)

[rosstimothy]

Thanks @codingllama!!!