ci: workspace mcpp bootstrap pin -> 2026.8.3.3 (released + indexed)

Safe to move now: v2026.8.3.3 is published on all four platforms, mirrored to
xlings-res (GitHub + GitCode, the GitCode copy verified by a real GET matching
the published sha256), and xim-pkgindex tracks it as latest.

Verified end to end: xlings install mcpp@2026.8.3.3 then xlings use resolves to
2026.8.3.3, and that released binary reproduces the B3 fix — ninja declares
bin/finalprobe.exe, the file exists, and a rebuild does not relink.

Author: Sunrisepeak

.xlings.json

@@ -1,5 +1,5 @@
 {
   "workspace": {
-    "mcpp": "2026.8.3.2"
+    "mcpp": "2026.8.3.3"
   }
 }