Only str->str mapping for filesToStage

src/uwtools/resources/FV3Forecast.jsonschema

@@ -4,17 +4,7 @@
       "minProperties": 1,
       "patternProperties": {
         "^.*$": {
-          "oneOf": [
-            {
-              "type": "string"
-            },
-            {
-              "items": {
-                "type": "string"
-              },
-              "type": "array"
-            }
-          ]
+          "type": "string"
         }
       },
       "type": "object"

src/uwtools/tests/drivers/test_forecast.py

@@ -435,14 +435,10 @@ def test_FV3Forecast_schema_filesToStage():
     assert "is not of type 'object'" in errors([])
     # A str -> str dict is ok:
     assert not errors({"file1": "/path/to/file1", "file2": "/path/to/file2"})
-    # A str -> List[str] dict is ok:
-    assert not errors({"dir": ["/path/to/file1", "/path/to/file2"]})
     # An empty dict is not allowed:
     assert "does not have enough properties" in errors({})
     # Non-string values are not allowed:
-    assert "not valid" in errors({"file1": True})
-    # Non-string list elements are not allowed:
-    assert "not valid" in errors({"dir": [88]})
+    assert "True is not of type 'string'" in errors({"file1": True})
 
 
 def test_FV3Forecast_schema_forecast_field_table(field_table_vals):