[systemd] install wget to download a dictionary for fuzz-json

[evverx]

No description provided.

[filbranden]

Note that when you pull gettext you're getting curl with it, so you might want to consider using it instead of wget, in which case this PR is not really blocking... (Though it might be a good idea to make that dependency on curl explicit if you start using it.)

Cheers,
Filipe

[evverx]

I vaguely remember that something happened to me in the past and since then I haven't relied on packages installed implicitly through Recommends :-), so it's indeed a good idea to make dependencies explicit. Regarding wget, it's already used in systemd/systemd#9782 and I'd rather not change it. Plus I believe this PR will be merged before I get to edit oss-fuzz.sh.