Upgrade to .NET 9.0 #302

Job	Run time
Test StringEnum Trimmed	43s
Timestamp	6s
Test Cloud Framework	2m 49s
Build macOS UEFS	1m 27s
Build Linux Shim	38s
Build Windows Pass 1	6m 38s
Build macOS Shim	38s
Build Windows Shim	1m 10s
Build Windows UEFS	3m 33s
Build and Test Libraries on Linux	6m 56s
Build Libraries on macOS	4m 53s
Build and Test Libraries on Windows	9m 29s
Build Linux Pass 1	6m 9s
Build macOS Pass 1	5m 39s
Build Windows Pass 2	7m 9s
Build Linux Pass 2	6m 19s
Build macOS Pass 2	5m 20s
Publish UET Container (with Wine)	0s
Publish UEFS Container	0s
Publish to GitHub	0s
Test Schema Generation	40s
Publish UET Container	0s
Publish to NuGet	0s
	1h 10m 16s

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