Enable the intl extension for "site health checker"

- see https://core.trac.wordpress.org/ticket/52654 for where this was added to site health

Author: yosifkit

Dockerfile.template

@@ -46,6 +46,7 @@ RUN set -ex; \
 	apk add --no-cache --virtual .build-deps \
 		$PHPIZE_DEPS \
 		freetype-dev \
+		icu-dev \
 		imagemagick-dev \
 		libjpeg-turbo-dev \
 		libpng-dev \
@@ -58,6 +59,7 @@ RUN set -ex; \
 	apt-get update; \
 	apt-get install -y --no-install-recommends \
 		libfreetype6-dev \
+		libicu-dev \
 		libjpeg-dev \
 		libmagickwand-dev \
 		libpng-dev \
@@ -82,6 +84,7 @@ RUN set -ex; \
 		bcmath \
 		exif \
 		gd \
+		intl \
 		mysqli \
 		zip \
 	; \