Update dependency DocumentFormat.OpenXml to 2.20.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
DocumentFormat.OpenXml	2.19.0 -> 2.20.0

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Release Notes

dotnet/Open-XML-SDK (DocumentFormat.OpenXml)

v2.20.0

Added

• Added DocumentFormat.OpenXml.Office.Drawing.Y2022.ImageFormula namespace
• Added DocumentFormat.OpenXml.Office.Word.Y2023.WordML.Word16DU namespace

Changed

• Marked OpenXmlSimpleType.TextValue as obsolete. This property was never meant to be used externally (#​1284)
• Marked OpenXmlPackage.Package as obsolete. This will be an implementation detail in future versions and won't be accessible (#​1306)
• Marked OpenXmlPackage.Close as obsolete. This will be removed in a later release, use Dispose instead (#​1371)
• Marked OpenXmlPackage.SaveAs as obsolete as it will be removed in a future version (#​1378)

Fixed

• Fixed incorrect file extensions for vbaProject files (#​1292)
• Fixed incorrect file extensions for ImagePart (#​1305)
• Fixed incorrect casing for customXml (#​1351)
• Fixed AddEmbeddedPackagePart to allow correct extensions for various content types (#​1388)

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