Bump nginx from 1.21.5 to 1.21.6 in /build (#2388)

Bumps nginx from 1.21.5 to 1.21.6.

---
updated-dependencies:
- dependency-name: nginx
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

build/Dockerfile

@@ -6,7 +6,7 @@ ARG DOWNLOAD_TAG=edge
 ARG DEBIAN_VERSION=bullseye-slim
 
 ############################################# Base image for Debian #############################################
-FROM nginx:1.21.5 AS debian
+FROM nginx:1.21.6 AS debian
 
 RUN apt-get update \
 	&& apt-get install --no-install-recommends --no-install-suggests -y libcap2-bin \