ci: add PR action to build and execute tests

.github/workflows/pull_request.yml

@@ -0,0 +1,36 @@
+name: pull_request
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+
+  complete:
+    if: always()
+    needs: [fmt, build-and-test]
+    runs-on: ubuntu-latest
+    steps:
+    - if: contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled')
+      run: exit 1
+
+  fmt:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - run: rustup update
+    - run: cargo fmt --all --check
+
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: stellar/actions/rust-cache@main
+    - run: rustup update
+    - run: rustup target add wasm32-unknown-unknown
+    - run: cargo install --locked --version 20.0.0-rc4 soroban-cli --features opt
+    - run: make test