[ci] Update PoliCheck exclusions (dotnet#7561)

Context: https://eng.ms/docs/security-compliance-identity-and-management-scim/security/azure-security/cloudai-security-fundamentals-engineering/security-integration/guardian-wiki/sdl-azdo-extension/policheck-build-task#adding-other-policheck-exclusions-from-the-policheck-scan

PoliCheck recently started failing due to changes in:

	external\android-api-docs\docs\Mono.Android\en\FrameworksIndex\xamarin-android-sdk-13.xml

Update the PoliCheck exclusion DB to include this path and term.