release: add binaries for riscv64gc-unknown-linux-gnu target

Note that we skip lz4/brotli/zstd tests on RISC-V.

The CI runs RISC-V tests using cross/QEMU emulation. The decompression
tools (lz4, brotli, zstd) are x86_64 binaries on the host that cannot
execute in the RISC-V QEMU environment.

Skip these three tests at compile-time on RISC-V to avoid test failures.
The -z/--search-zip functionality itself works correctly on real RISC-V
hardware where native decompression tools are available.

PR #3165

.github/workflows/ci.yml

@@ -95,6 +95,10 @@ jobs:
           os: ubuntu-latest
           rust: stable
           target: s390x-unknown-linux-gnu
+        - build: stable-riscv64
+          os: ubuntu-latest
+          rust: stable
+          target: riscv64gc-unknown-linux-gnu
         - build: macos
           os: macos-latest
           rust: nightly