fix: Update Docker image version reference in pull_request workflow

- Changed `WHOAMI_VERSION` to use the full SHA256 hash instead of a simple version tag.
- Adjusted `docker run` command to reference the updated `$WHOAMI_VERSION` variable.

Author: warnyul

.github/workflows/pull_request.yml

@@ -33,7 +33,7 @@ jobs:
           DOCKER_HOST: ${{ secrets.DOCKER_HOST }}
         run: |
           # renovate: datasource=docker depname=traefik/whoami versioning=docker
-          WHOAMI_VERSION="v1.10"
-          docker run -d -P --name whoami traefik/whoami:v1.10
+          WHOAMI_VERSION="43a68d10b9dfcfc3ffbfe4dd42100dc9aeaf29b3a5636c856337a5940f1b4f1c" # v1.10
+          docker run -d -P --name whoami traefik/whoami:"$WHOAMI_VERSION"
           docker stop whoami
           docker rm whoami