Update Rust crate p256 to 0.13

Author: renovate[bot]

Cargo.lock

@@ -18,7 +18,7 @@ lpc55_areas = { git = "https://github.com/oxidecomputer/lpc55_support", default-
 num-bigint = "0.4.6"
 # p256 v0.13 has a dependency that requires rustc 1.65 but we're pinned
 # to 1.64 till offline-keystore-os supports it
-p256 = "0.12"
+p256 = "0.13"
 pem-rfc7468 = { version = "0.7.0", features = ["alloc", "std"] }
 rand = "0.8.5"
 rand_chacha = "0.3.1"