Bug 42764: Update .codespell-ignore for valid technical terms

Add words to .codespell-ignore that codespell 2.4.x flags but are
valid technical terms, domain vocabulary, or proper names:

- checkin: core library circulation term (check-in as noun/verb)
- plack: Perl PSGI middleware framework (proper software name)
- requestor: COUNTER 5 standard term used in ERM usage statistics
- laf: EDIFACT 3-letter segment code
- vai/lamba: Unicode script and language names in character set data
- aas: acronym used in Cypress test support files
- carmel: contributor name in about.tt
- prfile: legacy variable abbreviation in C4/Creators/PDF.pm

Test plan:
1. Apply patch
2. prove xt/author/codespell.t
=> Test passes (or only genuine spelling errors remain)

Signed-off-by: Pedro Amorim <pedro.amorim@openfifth.co.uk>

.codespell-ignore

@@ -18,3 +18,12 @@ theses
 rouge
 connexion
 falsy
+aas
+carmel
+checkin
+laf
+lamba
+plack
+prfile
+requestor
+vai