contrib: update macOS SDK to Xcode-26.1.1-17B100

contrib/guix/README.md

@@ -261,7 +261,7 @@ details.
   Set the path where _extracted_ SDKs can be found. This is passed through to
   the depends tree. Note that this should be set to the _parent_ directory of
   the actual SDK (e.g. `SDK_PATH=$HOME/Downloads/macOS-SDKs` instead of
-  `$HOME/Downloads/macOS-SDKs/Xcode-12.2-12B45b-extracted-SDK-with-libcxx-headers`).
+  `$HOME/Downloads/macOS-SDKs/Xcode-26.1.1-17B100-extracted-SDK-with-libcxx-headers`).
 
   The path that this environment variable points to **must be a directory**, and
   **NOT a symlink to a directory**.