Docker Alpine 3.12 (#3025)

https://alpinelinux.org/posts/Alpine-3.12.0-released.html
With PHP 7.3.18 (from 7.3.17) (and Apache 2.4.43 unchanged).
No other significant change spotted

Docker/Dockerfile-Alpine

@@ -1,4 +1,4 @@
-FROM alpine:3.11
+FROM alpine:3.12
 
 ENV TZ UTC
 SHELL ["/bin/ash", "-eo", "pipefail", "-c"]