retrieve php packages from current ubuntu codename (#171)

* retrieve php packages from current ubuntu codename

This ensures the codename in the PPA matches the current distribution

* Update Dockerfile

Co-authored-by: Taylor Otwell <taylor@laravel.com>

runtimes/7.4/Dockerfile

@@ -18,7 +18,7 @@ RUN apt-get update \
     && echo "disable-ipv6" >> ~/.gnupg/dirmngr.conf \
     && apt-key adv --homedir ~/.gnupg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys E5267A6C \
     && apt-key adv --homedir ~/.gnupg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys C300EE8C \
-    && echo "deb http://ppa.launchpad.net/ondrej/php/ubuntu focal main" > /etc/apt/sources.list.d/ppa_ondrej_php.list \
+    && echo "deb http://ppa.launchpad.net/ondrej/php/ubuntu hirsute main" > /etc/apt/sources.list.d/ppa_ondrej_php.list \
     && apt-get update \
     && apt-get install -y php7.4-cli php7.4-dev \
        php7.4-pgsql php7.4-sqlite3 php7.4-gd \