:hammer: fix SupportedLanguage MergeBehaviour to upload SendGrid custom policy

[letusfly85]

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Hi, thank you for great repository!

We're now trying to upload SendGrid custom policy. But they aren't working by the following issue.

I found the following issue, so fixed XML. (I think that it is not easy to reach at the following comment who wants to integrate SendGrid 😅 )

https://github.com/azure-ad-b2c/samples/issues/304#issuecomment-965203925

Please check or give us feedback.

Thank you.