chore(deps): update nginx docker digest to ca871a8 (#216)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/main.yml

@@ -96,7 +96,7 @@ jobs:
     # start nginx as service to test validation via http-challenge local path
     services:
       nginx:
-        image: nginx@sha256:fb01117203ff38c2f9af91db1a7409459182a37c87cced5cb442d1d8fcc66d19
+        image: nginx@sha256:ca871a86d45a3ec6864dc45f014b11fe626145569ef0e74deaffc95a3b15b430
         volumes:
           - /tmp:/usr/share/nginx/html
         ports: