chore: run systest on nightly and beta as well

with `ctest2` we won't be blocked on gnzlbg/ctest#90.

Author: weihanglo

.github/workflows/main.yml

@@ -31,9 +31,7 @@ jobs:
       shell: bash
     - run: cargo test --no-default-features
     - run: cargo test
-    # skip systest on nightly because it requires the extprim crate which fails to compile on nightly rust
-    - run: if [[ "${{ matrix.rust }}" != "nightly" ]]; then cargo run --manifest-path systest/Cargo.toml; fi
-      shell: bash
+    - run: cargo run --manifest-path systest/Cargo.toml
     - run: cargo test --manifest-path git2-curl/Cargo.toml
 
   rustfmt: