ci: add a cargo-deny job and run CI on pull requests to main (#305)

CI gains a Cargo deny job (advisories, licenses, bans, sources) using the repository's deny.toml, and its pull_request trigger is limited to pull requests targeting main.

Co-authored-by: KairosMakki <332317221+KairosMakki@users.noreply.github.com>

.github/workflows/ci.yml

@@ -3,6 +3,8 @@ on:
   push:
     branches: [main]
   pull_request:
+    branches: [main]
+    types: [opened, synchronize, reopened]
   workflow_dispatch:
 
 concurrency:
@@ -69,6 +71,15 @@ jobs:
       - run: cargo build --locked -p ide-host --bin openidea-server --target x86_64-unknown-linux-musl
       - run: target/x86_64-unknown-linux-musl/debug/openidea-server --version
 
+  deny:
+    name: Cargo deny
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: taiki-e/install-action@cargo-deny
+      - run: cargo deny check
+
   frontend:
     name: Frontend
     runs-on: ubuntu-22.04