ci: replace cross with cargo-zigbuild for aarch64 cross-compilation

cross runs builds inside a Docker container, so the host-installed
Rust toolchain is not visible. Replace with cargo-zigbuild which
uses Zig as a cross-linker and runs directly on the host.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.gitea/workflows/release.yml

@@ -41,10 +41,14 @@ jobs:
         run: |
           curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain stable
           echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
-      - name: Install cross
-        run: cargo install cross --locked
+      - name: Install cargo-zigbuild
+        run: |
+          pip3 install ziglang --break-system-packages
+          cargo install cargo-zigbuild --locked
+      - name: Add aarch64 musl target
+        run: rustup target add aarch64-unknown-linux-musl
       - name: Build
-        run: cross build --release --target aarch64-unknown-linux-musl
+        run: cargo zigbuild --release --target aarch64-unknown-linux-musl
       - name: Create archive
         run: |
           VERSION=${GITHUB_REF_NAME#v}