boring-sys: include HPKE header file for bindgen #930

Job	Run time
Cross build from macOS to Linux (x86_64-unknown-linux-gnu)	1m 58s
Cross build from macOS to Linux (FIPS) (x86_64-unknown-linux-gnu)	3m 20s
clippy	8m 14s
rustfmt	5s
Test features	7m 18s
Test (stable)	2m 32s
Test FIPS integration	1m 47s
Test (arm-android)	2m 3s
Test (arm64-android)	2m 28s
Test (i686-android)	2m 3s
Test (x86_64-android)	1m 57s
Test (aarch64-ios)	2m 18s
Test (aarch64-ios-sim)	2m 17s
Test (x86_64-ios)	2m 56s
Test (i686-linux)	2m 25s
Test (arm-linux)	2m 26s
Test (aarch64-linux)	2m 38s
Test (arm64-macos)	2m 19s
Test (x86_64-macos)	2m 49s
Test (x86_64-mingw)	7m 11s
Test (i686-msvc)	7m 48s
Test (x86_64-msvc)	5m 29s
	1h 14m 21s

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