Upgrade to .NET 9.0 #301

Job	Run time
Test StringEnum Trimmed	35s
Timestamp	5s
Test Cloud Framework	1m 52s
Build macOS Shim	39s
Build Windows UEFS	3m 23s
Build Linux Pass 1	6m 41s
Build and Test Libraries on Windows	8m 45s
Build macOS Pass 1	3m 56s
Build Windows Pass 1	6m 46s
Build Linux Shim	35s
Build Windows Shim	1m 20s
Build macOS UEFS	1m 36s
Build and Test Libraries on Linux	7m 13s
Build Libraries on macOS	6m 31s
Build Windows Pass 2	6m 50s
Build macOS Pass 2	5m 21s
Build Linux Pass 2	6m 26s
Publish UET Container	0s
Publish UET Container (with Wine)	0s
Test Schema Generation	23s
Publish to NuGet	0s
Publish UEFS Container	0s
Publish to GitHub	0s
	1h 8m 57s

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