Install golang on macos runners

The macos-latest runner no longer comes with golang preinstalled.

Note that the fips build is not technically certified on macos,
but it is still nonetheless useful to defend the ability to
do `cargo test --all-features` on developer laptops.

.github/workflows/build.yml

@@ -56,6 +56,12 @@ jobs:
         if: runner.os == 'Windows'
         uses: seanmiddleditch/gha-setup-ninja@v4
 
+      - name: Install golang for aws-lc-fips-sys on macos
+        if: runner.os == 'MacOS'
+        uses: actions/setup-go@v5
+        with:
+          go-version: "1.22.2"
+
       - name: cargo build (debug; default features)
         run: cargo build --locked