Bump library/nginx in /backstage in the minor group across 1 directory

Bumps the minor group with 1 update in the /backstage directory: library/nginx.


Updates `library/nginx` from 1.27.3-alpine-slim to 1.27.4-alpine-slim

---
updated-dependencies:
- dependency-name: library/nginx
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backstage/Dockerfile

@@ -32,7 +32,7 @@ RUN mkdir packages/backend/dist/skeleton packages/backend/dist/bundle \
     && tar xzf packages/backend/dist/skeleton.tar.gz -C packages/backend/dist/skeleton \
     && tar xzf packages/backend/dist/bundle.tar.gz -C packages/backend/dist/bundle
 
-FROM docker.io/library/nginx:1.27.3-alpine-slim as frontend
+FROM docker.io/library/nginx:1.29.1-alpine-slim as frontend
 
 WORKDIR /app