feat(anvil): allow pass headers to `fork-url` #9206

Job	Run time
clippy	3m 56s
feature checks	3m 0s
doc tests	4m 31s
fmt	12s
forge fmt	9m 21s
build matrices	8s
build tests (ubuntu-latest, x86_64-unknown-linux-gnu)	9m 43s
test unit	46s
test integration (1/3)	4m 59s
test integration (2/3)	2m 37s
test integration (3/3)	4m 57s
test integration/issue-repros (1/2)	4m 46s
test integration/issue-repros (2/2)	47s
test integration/forge-std	1m 56s
test integration/external (1/2)	6m 52s
test integration/external (2/2)	2m 0s
	1h 0m 31s

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