ci: pin mcpp 2026.8.26.1 (#8)

The release this repository was already verified against, from its own branch
before the merge — seven repositories green, each checked to have logged
`under review: mcpp 2026.8.26.1`. This moves the pin to the published build so
the same check runs against what a user installs.

Author: Sunrisepeak

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ on:
         default: ""
 env:
   MCPP_SOURCE_REF: ${{ github.event.inputs.mcpp_ref || vars.MCPP_SOURCE_REF }}
-  MCPP_VERSION: 2026.8.25.2
+  MCPP_VERSION: 2026.8.26.1
   XLINGS_VERSION: v2026.8.17.2
   XLINGS_NON_INTERACTIVE: '1'