ci: bootstrap pin -> 2026.7.29.2 (the index no longer serves .1)

The routine post-release pin bump that 2026.7.29.2 never got. The index now
serves only .2, so anything bootstrapping from the pin dies with

  xlings: version '2026.7.29.1' not found for 'mcpp'
    available: 2026.7.29.2

ci-aarch64-fresh-install is where this surfaces, because it clones main at
runtime and builds it with the pinned mcpp — so the pin has to be right ON main,
not merely in the PR that notices. That workflow last ran on main 2026-07-28,
before either .1 or .2 existed, which is why the staleness went unseen.

Guard invariants hold: both pin sites agree, and the pin is not newer than the
version being built (main builds 2026.7.29.2).

Author: Sunrisepeak

.github/workflows/ci-fresh-install.yml

@@ -40,7 +40,7 @@ concurrency:
 # fails with `version not found` instead of silently testing an older
 # binary. Bump together with the .xlings.json workspace pin at release.
 env:
-  MCPP_PIN: '2026.7.29.1'
+  MCPP_PIN: '2026.7.29.2'
 
 jobs:
   # ──────────────────────────────────────────────────────────────────

.xlings.json

@@ -1,5 +1,5 @@
 {
   "workspace": {
-    "mcpp": "2026.7.29.1"
+    "mcpp": "2026.7.29.2"
   }
 }