PostgreSQL 15 minor fixes in protocol.sgml

Hello! I've come across some typos in protocol.sgml for PostgreSQL 15 so please have a look at the attached patch. I didn't include it in the patch but I also suggest removing single quotes around 'method' for the COMPRESSION option to help avoid confusion. (All the supported compression met

Typo in "43.9.1. Reporting Errors and Messages"?

The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/14/plpgsql-errors-and-messages.html Description: Towards the end of the "43.9.1. Reporting Errors and Messages" section (here https://www.postgresql.org/docs/current/plpgsql-errors-and-messag