fix(http1): use case-insensitive matching for trailer fields #3171

Job	Run time
Check Style	8s
semver	22s
Verify hyper.h is up to date	1m 49s
Check MSRV	20m 37s
features	1m 0s
Test C API (FFI)	34s
Test stable on macOS-latest	1m 37s
Test beta on macOS-latest	1m 39s
Test stable on windows-latest	2m 14s
Test stable on ubuntu-latest	1m 8s
minimal-versions	41s
udeps	28s
Test beta on windows-latest	2m 11s
Test cargo-c support (FFI)	17s
Test nightly on ubuntu-latest	1m 10s
Test with Miri	2m 21s
Test nightly on windows-latest	2m 32s
Test nightly on macOS-latest	2m 3s
Test beta on ubuntu-latest	1m 15s
Check exposed types	19s
Build docs	19s
CI is green	4s
	44m 48s

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