crypto/tls: FIPS 140-3 modes reject ECDSA w/ curve P-521/SHA-512 in TLS [1.24 backport]

[gopherbot]

@FiloSottile requested issue #71757 to be considered for backport to the next 1.24 minor release.

@gopherbot please open a backport change to Go 1.24 to revert the removal of P-521 in Go+BoringCrypto mode by cherry-picking CL 657095, as discussed above.

[gopherbot]

Change https://go.dev/cl/657135 mentions this issue: [release-branch.go1.24] crypto/tls: allow P-521 in FIPS 140-3 mode and Go+BoringCrypto

[gopherbot]

Closed by merging CL 657135 (commit bd1bc8a) to release-branch.go1.24.