Add semver check workflow to GitHub Actions (#160)

Author: PSeitz

.github/workflows/rust.yml

@@ -35,3 +35,11 @@ jobs:
       run: ./scripts/unicode.py && diff tables.rs src/tables.rs
     - name: Verify regenerated tests
       run: ./scripts/unicode_gen_breaktests.py && diff testdata.rs tests/testdata/mod.rs
+
+  semver:
+    name: semver
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Check semver
+        uses: obi1kenobi/cargo-semver-checks-action@v2