Modify the logic to rename.

.drone.yml

@@ -71,6 +71,7 @@ steps:
       - find content/ -type f -name '*.md' | grep -v '_index' | xargs -n 1 /usr/local/bin/tcardgen -f assets/font/ -o static/ogp/ -c assets/tcardgen.yaml > /dev/null
       - find static/ogp/ -type f -name '*.png' | xargs -I% -n 1 img2webp -lossy -q 50 % -o %.webp > /dev/null
       - find static/ogp/ -type f -name '*.png' | xargs --no-run-if-empty rm
+      - for webp in $(find static/ogp/ -type f -name *.webp); do mv ${webp} ${webp//.png./.}; done
 
   - name: hugo
     image: cibuilds/hugo:0.83.0