Incorrect permissions on /usr/lib/dart/bin on linux aarch64 2.14.4 build

[aebrahim]

This prevents the dart command from being used by a non-root user.

Steps to reproduce (on M1 mac mini)

docker run --rm -it dart:stable
root@84cc7db4dc9c:~# ls -l /usr/lib/dart
total 32
-rw-r--r--  1 root root 1502 Oct 13 02:12 LICENSE
-rw-r--r--  1 root root  981 Oct 13 02:12 README
drwx------  5 root root 4096 Oct 13 03:11 bin
-rw-r--r--  1 root root  928 Oct 13 03:00 dartdoc_options.yaml
drwxr-xr-x  3 root root 4096 Oct 13 02:54 include
drwxr-xr-x 26 root root 4096 Oct 13 03:04 lib
-rw-r--r--  1 root root   41 Oct 13 03:00 revision
-rw-r--r--  1 root root    7 Oct 13 03:00 version

This would be fixed by with RUN chmod 755 /usr/lib/dart/bin