net-tools package missing after series-upgrade following charm upgrade

After performing a series upgrade from bionic to focal, the net-tools package got removed and thus broke the post-series-upgrade hook of the keepalived charm (revision 98). Please see attached log.

The reason for this is because prior to the series upgrade a charm upgrade was performed to go from revision 28 to 98.

In revision 28, net-tools is not being installed:
@when_not('keepalived.package.installed')
def install_keepalived_package():
    ''' Install keepalived package '''
    status_set('maintenance', 'Installing keepalived')

    apt_update(fatal=True)
    apt_install('keepalived', fatal=True)

    set_flag('keepalived.package.installed')

While it is since revision 71:

@when_not('keepalived.package.installed')
def install_keepalived_package():
    ''' Install keepalived package '''
    status.maintenance('Installing keepalived')

    apt_update(fatal=True)
    apt_install(['keepalived', 'net-tools'], fatal=True)

    set_flag('keepalived.package.installed')

However, the upgrade_charm hook does not clear the flag 'keepalived.package.installed' and thus net-tools is not marked as just [installed], in my case it was set to [installed,auto-removable].

@hook('upgrade-charm')
def upgrade_charm():
    clear_flag('keepalived.started')
=> perhaps we just need to add clear_flag('keepalived.package.installed')