profiles: singularity: fix profile path

Commands used to check for issues:

    $ git ls-files 'etc/profile-a-l/' | grep 'etc/profile-a-l/[m-z]'
    etc/profile-a-l/singularity.profile
    $ git ls-files 'etc/profile-m-z/' | grep 'etc/profile-a-l/[a-l]'
    $

Command used to fix the path:

    $ git mv \
      etc/profile-a-l/singularity.profile \
      etc/profile-m-z/singularity.profile

Relates to #6463.