Refactor dimfilter to follow the new coding conventions

Author: seisman

pygmt/src/dimfilter.py

@@ -135,10 +135,10 @@ def dimfilter(grid, **kwargs):
         with Session() as lib:
             file_context = lib.virtualfile_from_data(check_kind=None, data=grid)
             with file_context as infile:
-                if "G" not in kwargs:  # if outgrid is unset, output to tempfile
-                    kwargs.update({"G": tmpfile.name})
-                outgrid = kwargs["G"]
-                arg_str = " ".join([infile, build_arg_string(kwargs)])
-                lib.call_module(module="dimfilter", args=arg_str)
+                if (outgrid := kwargs.get("G")) is None:
+                    kwargs["G"] = outgrid = tmpfile.name  # output to tmpfile
+                lib.call_module(
+                    module="dimfilter", args=build_arg_string(kwargs, infile=infile)
+                )
 
         return load_dataarray(outgrid) if outgrid == tmpfile.name else None