ci: Install gcc-aarch64-linux-gnu for gnd cross-compilation

Author: incrypto32

.github/workflows/gnd-binary-build.yml

@@ -64,6 +64,8 @@ jobs:
       - name: Build gnd binary (Unix/Mac)
         if: ${{ !startsWith(matrix.runner, 'windows') }}
         run: cargo build --bin gnd --release --target ${{ matrix.target }}
+        env:
+          CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER: aarch64-linux-gnu-gcc
 
       - name: Build gnd binary (Windows)
         if: startsWith(matrix.runner, 'windows')