chore(ci): add tests job for MSRV (1.55.0)

.github/workflows/rust.yml

@@ -17,13 +17,36 @@ env:
   RUST_BACKTRACE: short
 
 jobs:
-  tests:
+  tests-msrv-version:
     runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 0
+    - name: Install Rust toolchain (minimal supported rust version)
+      uses: dtolnay/rust-toolchain@1.55.0
+    - name: print rustc version
+      run: rustc --version
+    - name: Run tests
+      run: |
+        pushd borsh
+        cargo test --no-run
+        cargo test
+        cargo test --no-default-features
+        cargo test --all-features
+        popd
+        cargo test --workspace
+
+  tests-stable:
+    runs-on: ubuntu-20.04
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - name: print rustc version
+      run: rustc --version
     - name: Run tests
       run: |
         pushd borsh