fix(ci): install cargo-zigbuild on Linux CI runners

mise.toml restricts cargo-zigbuild to macOS only. Explicitly install it
in the publish workflow so cross-compilation works on ubuntu-latest.

Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com>
Signed-off-by: Paolo Dettori <dettori@us.ibm.com>

Author: pdettori

.github/workflows/publish.yml

@@ -35,6 +35,9 @@ jobs:
           rustup target add x86_64-unknown-linux-gnu
           rustup target add aarch64-unknown-linux-gnu
 
+      - name: Install cargo-zigbuild
+        run: cargo install cargo-zigbuild
+
       - name: Cache Rust target and registry
         uses: Swatinem/rust-cache@v2
         with:
@@ -118,6 +121,9 @@ jobs:
           rustup target add x86_64-unknown-linux-gnu
           rustup target add aarch64-unknown-linux-gnu
 
+      - name: Install cargo-zigbuild
+        run: cargo install cargo-zigbuild
+
       - name: Cache Rust target and registry
         uses: Swatinem/rust-cache@v2
         with: