docs: fix clumsy grammar in the scripts-based testsuite chapter * doc/automake.texi (Scripts-based Testsuites): "We'll have later" is a rare example of English in the Automake manual clearly not written by a native English-speaker: while comprehensible, it can be better formulated. Copyright-paperwork-exempt: yes Signed-off-by: Nick Alcock <nick.alcock@oracle.com> Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>