Use Claude Code GitHub Action in issue-bot workflow

- Replace `npm install -g @anthropic-ai/claude-code` + `claude -p` with
  `anthropics/claude-code-action@v1`
- Move inline ${{ }} step output to env var in Update PR description step

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ondrejmirtes

.github/workflows/issue-bot.yml

@@ -281,31 +281,26 @@ jobs:
         if: steps.check.outputs.skip != 'true'
         uses: "ramsey/composer-install@v3"
 
-      - name: "Install Claude Code"
-        if: steps.check.outputs.skip != 'true'
-        run: npm install -g @anthropic-ai/claude-code
-
       - name: "Save HEAD before generation"
         if: steps.check.outputs.skip != 'true'
         id: before
-        run: echo "sha=$(git rev-parse HEAD)" >> "$GITHUB_OUTPUT"
-
-      - name: "Generate regression tests"
-        if: steps.check.outputs.skip != 'true'
-        env:
-          CLAUDE_CODE_OAUTH_TOKEN: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           git config user.name "phpstan-bot"
           git config user.email "ondrej+phpstanbot@mirtes.cz"
+          echo "sha=$(git rev-parse HEAD)" >> "$GITHUB_OUTPUT"
 
-          claude -p \
-            --model claude-opus-4-6 \
-            "Read the file ./tmp/step-summary.md which contains the Issue Bot step summary from CI in Markdown format. Interpret this Markdown to figure out which GitHub issues need regression tests added. For each affected issue (where behavior changed), run /regression-test with the issue number.
+      - name: "Generate regression tests"
+        if: steps.check.outputs.skip != 'true'
+        uses: anthropics/claude-code-action@v1
+        with:
+          claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
+          claude_args: "--model claude-opus-4-6"
+          prompt: |
+            Read the file ./tmp/step-summary.md which contains the Issue Bot step summary from CI in Markdown format. Interpret this Markdown to figure out which GitHub issues need regression tests added. For each affected issue (where behavior changed), run /regression-test with the issue number.
 
-          Also read the diff of this branch to see what has already been done. The primary fixed issue will already have a test committed. The Issue Bot step summary might mention other fixed issues, so please add regression tests for those.
+            Also read the diff of this branch to see what has already been done. The primary fixed issue will already have a test committed. The Issue Bot step summary might mention other fixed issues, so please add regression tests for those.
 
-          Do not create a branch or push - this will be handled automatically."
+            Do not create a branch or push - this will be handled automatically.
 
       - name: "Push"
         if: steps.check.outputs.skip != 'true'
@@ -321,8 +316,8 @@ jobs:
         if: steps.check.outputs.skip != 'true'
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BEFORE_SHA: ${{ steps.before.outputs.sha }}
         run: |
-          BEFORE_SHA="${{ steps.before.outputs.sha }}"
           CURRENT_SHA="$(git rev-parse HEAD)"
 
           if [ "$BEFORE_SHA" = "$CURRENT_SHA" ]; then