docs: point the PR checklist at the gate the workflow documents

The checklist asked for `composer ci`, which is not the pre-push gate.
`ci` runs cgl, phpstan, unit, integration and fuzzy; `make gate` runs
cgl, phpstan, unit, fuzzy, rector pinned to PHP 8.2 and functional
against sqlite, plus the CHANGELOG check. Rector and the functional
suite are exactly the two the Makefile comment names as the ones that
get skipped by hand and are then found by the CI matrix a push later.

So the box a contributor ticked certified a narrower set than the
workflow in AGENTS.md prescribes, and the difference was invisible at
the point of ticking it. Both targets stay — they answer different
questions — but the checklist now names the one that gates a push.

Assisted-by: claude-code:claude-opus-5
Agent-Session: https://claude.ai/code/session_015QXXkquh2eQNBiTYA39Wss host=32116e
Signed-off-by: Sebastian Mendel <github@sebastianmendel.de>

Author: CybotTM

.github/PULL_REQUEST_TEMPLATE.md

@@ -17,7 +17,7 @@
 ## Checklist
 
 - [ ] My code follows the project's coding standards
-- [ ] I have run `composer ci` and all checks pass
+- [ ] I have run `make gate` and all checks pass (not `composer ci` — that set omits Rector and the functional suite)
 - [ ] I have added tests that prove my fix/feature works
 - [ ] I have updated the documentation accordingly
 - [ ] I have added a `CHANGELOG.md` entry under `## [Unreleased]`