Annotate `CheckSystemVersion` with `[Supported|Unsupported]OSPlatformGuard` attribute

[Youssef1313]

See dotnet/roslyn-analyzers#6189 (comment) for info

[chamons]

Turns out this actually is a roslyn-analzyer bug after discussing it with the engineer, filing shortly.

[chamons]

Moved to dotnet/roslyn-analyzers#6204

[rolfbjarne]

Reopening because:

• The required support has been implemented in .NET 7 (although it won't ship in the initial .NET 7 release): Support UIDevice.CheckSystemVersion from Microsoft.iOS/Catalyst workloads or provide SupportedOSPlatformGuard/UnsupportedOSPlatformGuard that supports dynamic versions roslyn-analyzers#6204
• We also need changes on our side.