Merge #1691

1691: update webmails to PHP 7.4 r=mergify[bot] a=lub

## What type of PR?

update

## What does this PR do?

### Related issue(s)

## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [ ] In case of feature or enhancement: documentation updated accordingly
- [ ] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.



I think it's a minor change, which needs no changelog.

I've tested rainloop, would be great if someone could test roundcube, because I don't use it.

Co-authored-by: lub <git@lubiland.de>

webmails/rainloop/Dockerfile

@@ -2,10 +2,10 @@ ARG ARCH=""
 ARG QEMU=other
 
 # NOTE: only add file if building for arm
-FROM ${ARCH}php:7.3-apache as build_arm
+FROM ${ARCH}php:7.4-apache as build_arm
 ONBUILD COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
 
-FROM ${ARCH}php:7.3-apache as build_other
+FROM ${ARCH}php:7.4-apache as build_other
 
 FROM build_${QEMU}
 #Shared layer between rainloop and roundcube

webmails/roundcube/Dockerfile

@@ -1,10 +1,10 @@
 # NOTE: only add file if building for arm
 ARG ARCH=""
 ARG QEMU=other
-FROM ${ARCH}php:7.3-apache as build_arm
+FROM ${ARCH}php:7.4-apache as build_arm
 ONBUILD COPY --from=balenalib/rpi-alpine:3.10 /usr/bin/qemu-arm-static /usr/bin/qemu-arm-static
 
-FROM ${ARCH}php:7.3-apache as build_other
+FROM ${ARCH}php:7.4-apache as build_other
 
 FROM build_${QEMU}
 #Shared layer between rainloop and roundcube