Fix typo in operation name from 'substract' to 'subtract' in ACCESS-ESM1.6 mappings

Author: rbeucher

src/access_moppy/mappings/ACCESS-ESM1.6_mappings.json

@@ -2562,7 +2562,7 @@
             ],
             "calculation": {
                 "type": "formula",
-                "operation": "substract",
+                "operation": "subtract",
                 "args": [
                     "fld_s03i262",
                     "fld_s03i293"