Bump alpine from 3.14.3 to 3.15.0

Bumps alpine from 3.14.3 to 3.15.0.

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

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

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.14.3
+FROM alpine:3.15.0
 
 ARG OPENVPN_PACKAGE_VERSION=2.5.2-r0
 RUN apk add --no-cache openvpn=$OPENVPN_PACKAGE_VERSION