[CI] move LLVM to 22

Address comments made in commit:
`2a92a831 (Fix CI on MacOS (#3813), 2026-05-13)`

Author: rchildre3

.github/workflows/build_and_test.yml

@@ -14,8 +14,7 @@ env:
   AFL_PIZZA_MODE: "-1" # this is sad, I know, but it breaks on a certain spring day otherwise :(
   CARGO_TERM_COLOR: always
   CARGO_NET_GIT_FETCH_WITH_CLI: true
-  # FIXME: please unpin macos rust stable toolchain once LLVM is bumped to version 22
-  MAIN_LLVM_VERSION: 21
+  MAIN_LLVM_VERSION: 22
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -975,7 +974,7 @@ jobs:
   macos:
     runs-on: macOS-latest
     steps:
-      - uses: dtolnay/rust-toolchain@1.94.1
+      - uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy
       - name: Install nightly