software/jstestnode: use a $FONTCONFIG_FILE

without valid fonts, firefox refuses to start
2 jobs for fix/jstestnode-fontconfig
Status Job ID Name Coverage
  External
running SlapOS.SlapRunner.ResilienceTest-Master.ERP5

42020:45:45

running SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

42020:44:42