Tag the 0.7.4 release

[dtolnay]

This tag is missing. Pretty sure the commit that was released is 8378267.

[dtolnay]

Release notes:

• Adds skip_deserializing attribute (feat(codegen) skip_deserializing #265)
• Adds Deserialize impl for Box<[T]> (fix(impls): Deserialize impl for Box<[T]> #290)
• Fields with skip_serializing are no longer required to implement the Serialize trait (feat(codegen): Inhibit generic bounds if skip_serializing #260, feat(codegen): Infer Default and Deserialize bounds correctly #285)
• A bound of std::default::Default is inferred for fields that use the default attribute (feat(codegen): Infer Default and Deserialize bounds correctly #285)
• Supports codegen for structs that use defaulted generic type params (fix(codegen): Discard type defaults from impl generics #295)
• Supports extern crate serde not in the top-level module (fix(codegen): Support extern crate serde not in toplevel module #298)

[dtolnay]

https://github.com/serde-rs/serde/releases/tag/v0.7.4