Update mypy to 1.20.0 (#15588)

stubs/openpyxl/@tests/stubtest_allowlist.txt

@@ -8,10 +8,6 @@ openpyxl.descriptors.DEBUG
 # The actual runtime definition depends on what else is installed
 # (lxml, defusedxml, et_xmlfile)
 openpyxl.xml._functions_overloads
-openpyxl.xml.functions.Element.__iter__
-openpyxl.xml.functions.fromstring
-openpyxl.xml.functions.iterparse
-openpyxl.xml.functions.tostring
 
 # Requires numpy to be installed
 openpyxl.utils.dataframe
@@ -41,10 +37,8 @@ openpyxl\.descriptors\.(base\.)?Typed\.allow_none
 # Inconsistent methods because
 # - using the default value results in an error because of the runtime type-guards
 # - or, keyword arguments are explicitly specified
-openpyxl.cell.Cell.__init__
 openpyxl.cell.cell.Cell.__init__
 openpyxl.cell.cell.WriteOnlyCell
-openpyxl.cell.WriteOnlyCell
 openpyxl.cell.text.PhoneticProperties.__init__
 openpyxl.cell.text.PhoneticText.__init__
 openpyxl.chart.axis._BaseAxis.__init__