ttcn3-pgw-test: fix jenkins.sh: do not use bash specific syntax
On some systems /bin/sh is a symbolic link to bash, so everything
works fine. On systems where /bin/sh is a real sh, copy fails:
cp: cannot access 'open5gs-{smf,upf,nrf}.yaml': No such file or directory
Change-Id: I64e9ddefdb6deb21b3bce3bc1af875a92919e6c9
Related: SYS#5602
