Infra: Fix directive name in PR template (#3286)

Author: encukou

.github/PULL_REQUEST_TEMPLATE/Mark a PEP Final.md

@@ -9,4 +9,4 @@ If you're unsure about something, just leave it blank and we'll take a look.
 * [ ] Any substantial changes since the accepted version approved by the SC/PEP delegate
 * [ ] Pull request title in appropriate format (``PEP 123: Mark Final``)
 * [ ] ``Status`` changed to ``Final`` (and ``Python-Version`` is correct)
-* [ ] Canonical docs/spec linked with a ``canonical-doc`` directive (or ``pypa-spec``, for packaging PEPs)
+* [ ] Canonical docs/spec linked with a ``canonical-doc`` directive (or ``canonical-pypa-spec``, for packaging PEPs)