Remove stale Yarn apt source from base image

The base image (mcr.microsoft.com/devcontainers/php:8.2) ships with a
Yarn apt repository whose GPG key (62D54FD4003F6525) can no longer be
verified. This causes apt-get update to fail during devcontainer feature
installation (e.g. sshd), breaking container builds.

The Yarn apt source is unused — nothing in this image installs yarn from
apt — so it is safe to remove.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kurowski

Dockerfile

@@ -1,5 +1,8 @@
 FROM mcr.microsoft.com/devcontainers/php:8.2
 
+# Remove stale Yarn apt source from base image (expired GPG key breaks apt-get update)
+RUN rm -f /etc/apt/sources.list.d/yarn.list
+
 # Change default umask and add user to web group so we can share write permission on web files
 RUN sed -i 's/^UMASK\s*022/UMASK 002/' /etc/login.defs
 RUN usermod -aG www-data vscode