Add create-release workflow (#15)

.github/workflows/create-release.yml

@@ -0,0 +1,66 @@
+name: Create Release
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  create-release:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 2  # Fetch the last two commits for comparison
+
+      - name: Check if lean-toolchain has changed
+        id: check_file_change
+        run: |
+          # Check if the lean-toolchain file was modified in the last commit
+          if git diff --name-only HEAD~1 HEAD | grep -q "^lean-toolchain$"; then
+            echo "CHANGED=true" >> $GITHUB_ENV
+          else
+            echo "CHANGED=false" >> $GITHUB_ENV
+          fi
+
+      - name: Exit if lean-toolchain did not change
+        if: env.CHANGED != 'true'
+        run: echo "No changes in lean-toolchain. Skipping release."
+
+      - name: Read Lean version from lean-toolchain
+        if: env.CHANGED == 'true'
+        id: get_version
+        run: |
+          # Extract the version from the lean-toolchain file (everything after the colon)
+          LEAN_VERSION=$(cut -d ':' -f2 < lean-toolchain | tr -d '[:space:]')
+          echo "tag_name=${LEAN_VERSION}" >> $GITHUB_ENV
+
+      - name: Create Git tag
+        if: env.CHANGED == 'true'
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git tag -a ${{ env.tag_name }} -m "Release ${{ env.tag_name }}"
+          git push origin ${{ env.tag_name }}
+
+      - name: Create GitHub Release
+        if: env.CHANGED == 'true'
+        uses: actions/github-script@v7
+        env:
+            tag_name: ${{ env.tag_name }}
+            GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          script: |
+            const tagName = process.env.tag_name;
+            const releaseName = `${tagName}`;
+            await github.rest.repos.createRelease({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              tag_name: tagName,
+              name: releaseName,
+              body: `Automated release for Lean version ${tagName}`,
+              draft: false,
+              prerelease: false
+            });