fedora-arm-minimal: increase root partition size
    
    The image creation currently silently fails on Fedora 33 because the
    kernel scriptlet is unable to create the initramfs:
    
      cp: error writing '/var/tmp/dracut.SqTiPj/initramfs/lib/libbrotlicommon.so.1.0.7': No space left on device
      dracut-install: ERROR: failed to install '/lib/libbrotlicommon.so.1' for '/var/tmp/dracut.SqTiPj/initramfs/usr/sbin/rngd'
      ...
    
    I'm not entirely sure how much space is actually needed. Hopefully not
    more than 100M though.