FileMiddleware will provide correct mime type for non lowercase file extensions #2121

Job	Run time
linux (swift:5.9)	3m 43s
linux (swift:5.10)	3m 38s
linux (swift:6.0)	3m 42s
linux (swiftlang/swift:nightly-6.1-jammy)	3m 40s
	14m 43s

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