[release-branch.go1.19] crypto/x509: allow BoringCrypto to use 4096-bit keys

[release-branch.go1.19] crypto/x509: allow BoringCrypto to use 4096-bit keys

FIPS-140 has been updated to allow 4096-bit RSA keys.
Allow them in certificate processing.

For #41147.
Fixes #56672.

Change-Id: I4c6bcb1b137a200dfe70cebc605ae57f49871184
Reviewed-on: https://go-review.googlesource.com/c/go/+/447655
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/449016