Fix Docker workflow failing on PRs and switch to fastcrc (YosysHQ#469)

Skip Docker Hub login on pull_request events where the DOCKERHUB_TOKEN
secret is not available. Replace crc/crcmod with fastcrc in Dockerfile.

Co-authored-by: Pepijn de Vos <pepijndevos@Pepijns-MacBook-Pro.local>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

.github/workflows/docker-build.yml

@@ -38,6 +38,7 @@ jobs:
           echo "Using Gowin IDE version: $VERSION"
 
       - name: Log in to Docker Hub
+        if: github.event_name == 'push'
         uses: docker/login-action@v3
         with:
           username: pepijndevos

Dockerfile

@@ -14,7 +14,7 @@ RUN apt-get update && \
     apt-get install -y xxd && \
     echo "B016: EB" | xxd -r -g 0 - ${GOWINHOME}/IDE/bin/gw_sh
 
-RUN pip install --no-cache-dir crc numpy crcmod msgspec
+RUN pip install --no-cache-dir numpy fastcrc msgspec
 
 WORKDIR /usr/src/apicula