nss: update to 3.55

Note that this says the NSPR dependency is bumped. I didn't encounter
any problems with 2.46. It seems to be a change that their automation
was updated to the newer version.

NSS 3.55

    P384 and P521 elliptic curve implementations are replaced with verifiable implementations from Fiat-Crypto and ECCKiila. Special thanks to the Network and Information Security Group (NISEC) at Tampere University.
    PK11_FindCertInSlot is added. With this function, a given slot can be queried with a DER-Encoded certificate, providing performance and usability improvements over other mechanisms. See Bug 1649633 for more details.
    DTLS 1.3 implementation is updated to draft-38. See Bug 1647752 for details.
    NSPR dependency updated to 4.27.

NSS 3.54

    Support for TLS 1.3 external pre-shared keys (Bug 1603042).
    Use ARM Cryptography Extension for SHA256, when available. (Bug 1528113).

(maya)