fix: allow bindgen to load libclang in static builds

[gsmlg]

Summary

• disable musl crt-static for the static build Cargo invocation so bindgen can dlopen libclang
• keep LIBCLANG_PATH pointing at Alpine's libclang package
• cover the bindgen/libclang release-script behavior in the focused static NIF release test

Verification

• elixir -e 'ExUnit.start(); Code.require_file("test/denox_static_nif_release_test.exs")'
• sh -n .github/scripts/build-static-nif.sh
• mix format --check-formatted test/denox_static_nif_release_test.exs
• git diff --check

Follow-up for Release run 29013846958: aarch64 static musl built V8 and found libclang, but bindgen failed to dlopen it with musl crt-static enabled.