fix(ci): drop invalid RENOVATE_CONFIG_FILE inline JSON

RENOVATE_CONFIG_FILE must point to a config file on disk; the inline
JSON string made Renovate abort with 'Custom config file ... must exist'.
The repo-root renovate.json (which already extends config:recommended)
is picked up automatically, so the env var is not needed.

.gitea/workflows/renovate.yaml

@@ -21,7 +21,6 @@ jobs:
             -e RENOVATE_AUTODISCOVER=false \
             -e RENOVATE_REPOSITORIES="${{ gitea.repository }}" \
             -e RENOVATE_ONBOARDING=false \
-            -e RENOVATE_CONFIG_FILE='{"extends":["config:recommended"]}' \
             -e LOG_LEVEL=info \
             -v /var/tmp/renovate-cache:/tmp/renovate-cache \
             ghcr.io/renovatebot/renovate:latest