[PHP] Bump to 7.4.21

CERTFR-2021-AVI-501

apaches/Dockerfile

@@ -1,4 +1,4 @@
-from php:7.4.20-apache
+from php:7.4.21-apache
 
 RUN a2enmod remoteip
 RUN echo "RemoteIPHeader X-Forwarded-For" > /etc/apache2/conf-available/remoteip.conf

apaches/docker-compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 services:
   apache:
       build: .
-      image: my_apache:7.4.20
+      image: my_apache:7.4.21
       container_name: apache
       networks:
         - proxy

apaches/maintenance/docker-compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 services:
   web:
       build: ..
-      image: my_apache:7.4.20
+      image: my_apache:7.4.21
       container_name: maintenance
       networks:
         - proxy

apaches/testing/docker-compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 services:
   apache-test:
       build: ..
-      image: my_apache:7.4.20
+      image: my_apache:7.4.21
       container_name: apache-test
       networks:
         - proxy