[benchmarks] tidy up files in the benchmarks directory (#210)

Author: odow

.github/workflows/format_check.yml

@@ -20,8 +20,7 @@ jobs:
           using Pkg
           Pkg.add(PackageSpec(name="JuliaFormatter", version="2"))
           using JuliaFormatter
-          format("src", verbose=true)
-          format("test", verbose=true)
+          format("."; verbose = true)
           out = String(read(Cmd(`git diff`)))
           if isempty(out)
               exit(0)