tests: don't use single-argument map

Single-argument `map` is being removed from Julia after an analysis
of registered packages found that the change doesn't break the
functionality of any package. See JuliaLang/julia#35293 and
JuliaLang/julia#52631

That said, the Julia change breaks your test suite, so here's a PR that
fixes that.

Author: nsajko

test/run.jl

@@ -73,7 +73,8 @@ end
     f₂() = read("file", String)
     h = Job(Thunk(sleep, 3); username="me", name="h")
     i = Job(Thunk(f₁, 1001); username="me", name="i")
-    j = ConditionalJob(Thunk(map, f₂); username="he", name="j")
+    caller = f -> f()
+    j = ConditionalJob(Thunk(caller, f₂); username="he", name="j")
     [h, i] .→ Ref(j)
     wf = Workflow(j)
     @test unique(wf) == collect(wf)