Update headers requirement from 0.3.5 to 0.4.0 #559

Job	Run time
Documentation	18s
Lints	41s
Minimal Depencency Versions (MSRV)	4m 21s
Build (aarch64-unknown-linux-gnu)	3m 8s
Memory leaks	3m 45s
Build (x86_64-pc-windows-gnu)	3m 22s
Minimal Dependency Versions	43s
Build (x86_64-unknown-linux-gnu)	2m 57s
Minimum Supported Rust Version	4m 13s
Semantic Versioning	23s
Test Suite	3m 44s
Publish version	0s
	27m 35s

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