Bump alpine from 3.20.2 to 3.20.3 in /web

Bumps alpine from 3.20.2 to 3.20.3.

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

Signed-off-by: dependabot[bot] <support@github.com>

web/Dockerfile

@@ -1,5 +1,5 @@
 # syntax = docker/dockerfile:1.3
-FROM alpine:3.20.2
+FROM alpine:3.20.3
 
 # Add requirements file.
 COPY requirements.txt /tmp/

web/Dockerfile.dev

@@ -1,5 +1,5 @@
 # syntax = docker/dockerfile:1.3
-FROM alpine:3.20.2
+FROM alpine:3.20.3
 
 ARG POSTORIUS_REF
 ARG HYPERKITTY_REF