langref: define the inferred error set syntax more explicitly
langref: define the inferred error set syntax more explicitly

This edit allows the reader to understand the syntax this section is talking about more quickly – they don’t have to read the whole code block and understand which part of it demonstrates the feature being described.

Affects https://ziglang.org/documentation/master/#Inferred-Error-Sets

andrewrk/zig,andrewrk/zig