Fix warning typo (#62583)

Author: matiaslindgren

pandas/core/arrays/string_.py

@@ -172,7 +172,7 @@ def __init__(
             warnings.warn(
                 "The 'pyarrow_numpy' storage option name is deprecated and will be "
                 'removed in pandas 3.0. Use \'pd.StringDtype(storage="pyarrow", '
-                "na_value-np.nan)' to construct the same dtype.\nOr enable the "
+                "na_value=np.nan)' to construct the same dtype.\nOr enable the "
                 "'pd.options.future.infer_string = True' option globally and use "
                 'the "str" alias as a shorthand notation to specify a dtype '
                 '(instead of "string[pyarrow_numpy]").',