test_infra: Enable cross-build for "musl" and "aarch64" targets

With enabling the `vendered-openssl` feature, we can now cross-build the
`test_infra` crate for  "musl" and "aarch64" targets. In this way, we
can remove the `test_infra` crate from the "exclude" list, so that this
crate can be checked and processed by "cargo clippy" and "cargo fmt".

More details can be found: https://docs.rs/openssl/latest/openssl/#vendored

As 'musl-gcc' is required, this commit also installs the `musl-tools`
package for our "build" github action on the musl target [1].

[1] https://github.com/actions-rs/toolchain/issues/102

Signed-off-by: Bo Chen <chen.bo@intel.com>

.github/workflows/build.yaml

@@ -22,6 +22,9 @@ jobs:
         with:
           fetch-depth: 0
 
+      - name: Install musl-gcc
+        run: sudo apt install -y musl-tools
+
       - name: Install Rust toolchain (${{ matrix.rust }})
         uses: actions-rs/toolchain@v1
         with: