Update `validators` dep

[hirschenberger]

There's a deprecation warning when compiling with the phone-number feature.

warning: the following packages contain code that will be rejected by a future version of Rust: quick-xml v0.17.2

It comes from the dependency chain:

quick-xml v0.17.2
└── phonenumber v0.2.5+8.11.3
    └── validators v0.20.19
        └── vcard v0.4.13

[hirschenberger]

@magiclen Can you please update the validators dependency before my code breaks?