Add an architecture with libc::c_char == u8 build to CI (RustPython#4704)

* Add compilation check for c_char is u8 arch
* install gcc-aarch64-linux-gnu for check

Author: patrickzbhe

.github/workflows/ci.yaml

@@ -192,6 +192,15 @@ jobs:
       - name: Check compilation for android
         run: cargo check --target aarch64-linux-android
 
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          target: aarch64-unknown-linux-gnu
+
+      - name: Install gcc-aarch64-linux-gnu
+        run: sudo apt install gcc-aarch64-linux-gnu
+      - name: Check compilation for aarch64 linux gnu
+        run: cargo check --target aarch64-unknown-linux-gnu
+
       - uses: dtolnay/rust-toolchain@stable
         with:
           target: i686-unknown-linux-musl