pygmt.grdfill: Fix PyGMT versions in FutureWarnings for "constant_fill" and "hole" (#4338)

Author: yvonnefroehlich

pygmt/src/grdfill.py

@@ -78,9 +78,9 @@ def _validate_params(
 @fmt_docstring
 # TODO(PyGMT>=0.19.0): Remove the deprecated 'no_data' parameter.
 # TODO(PyGMT>=0.19.0): Remove the deprecated 'mode' parameter.
-@deprecate_parameter("no_data", "hole", "v0.18.0", remove_version="v0.20.0")
+@deprecate_parameter("no_data", "hole", "v0.15.0", remove_version="v0.19.0")
 @deprecate_parameter(
-    "constantfill", "constant_fill", "v0.15.0", remove_version="v0.19.0"
+    "constantfill", "constant_fill", "v0.18.0", remove_version="v0.20.0"
 )
 @deprecate_parameter("gridfill", "grid_fill", "v0.18.0", remove_version="v0.20.0")
 @deprecate_parameter(