Update nginxinc/nginx-unprivileged Docker tag to v1.28.0

Author: renovate[bot]

openapi/Earthfile

@@ -31,7 +31,7 @@ explorer-build:
     SAVE ARTIFACT node_modules/openapi-explorer/dist/browser/openapi-explorer.min.js
 
 explorer:
-    FROM nginxinc/nginx-unprivileged:1.27.4-alpine
+    FROM nginxinc/nginx-unprivileged:1.28.0-alpine
 
     COPY v1/schemas /usr/share/nginx/html/schemas/
     COPY v1/odmApi.yaml /usr/share/nginx/html/