aspell: disable parrallel build

Sometimes we observe:

    /usr/bin/ld: cannot find -laspell
    collect2: error: ld returned 1 exit status
    libtool: install: error: relink `email-filter.la' with the above command before installing it
    Makefile:960: recipe for target 'install-filterLTLIBRARIES' failed
1 job for fix/erp5-aspell-parrallel-build in 0 seconds
Status Job ID Name Coverage
  External
failed SLAPOS-SR-TEST-JEROME-WIP

05:21:56