allow only importing national data if a column doesn't matches a value

Some sheets have data for, e.g. multiple years in and we only want one
of them so update the skip logic to allow for skipping unless the column
matches versus skipping if the column does not match

crowdsourcer/management/commands/import_national_data.py

@@ -190,7 +190,15 @@ def import_answers(self, user, rt, df, q, details):
             for _, row in df.iterrows():
                 if details.get("skip_check", None) is not None:
                     skip_check = details["skip_check"]
-                    if row[skip_check["col"]] == skip_check["val"]:
+                    if (
+                        skip_check.get("unless_match")
+                        and row[skip_check["col"]] != skip_check["val"]
+                    ):
+                        continue
+                    elif (
+                        not skip_check.get("unless_match")
+                        and row[skip_check["col"]] == skip_check["val"]
+                    ):
                         continue
 
                 gss_col = details.get("gss_col", "Local Authority Code")