Add -s flag to wgrib2 -lon extraction for inventory output

Without -s, wgrib2 -lon only outputs msg:offset:lon=X,lat=Y,val=Z
with no variable name or level. The -s flag adds the short inventory
(d=DATE:VAR:LEVEL:...) so the parser can identify which variable
each value belongs to.

lib/microwaveprop/weather/grib2/wgrib2.ex

@@ -372,7 +372,7 @@ defmodule Microwaveprop.Weather.Grib2.Wgrib2 do
         ["-lon", "#{normalize_lon(lon)}", "#{lat}"]
       end)
 
-    args = [grib_path, "-match", match_pattern] ++ lon_args
+    args = [grib_path, "-s", "-match", match_pattern] ++ lon_args
 
     case System.cmd(wgrib2_path(), args, stderr_to_stdout: true) do
       {output, 0} ->