[BUG] overmind-graphql type is broken

[SergeiKalachev]

@christianalfoni Hello!

I discovered a bug in overmind-graphql package. I upgraded all packages to the latest versions:

    "overmind": "28.0.1",
    "overmind-graphql": "8.0.1",
    "overmind-react": "29.0.1",

After the upgrade I see TS error in my gql files where gql function from overmind-graphql is used:

Argument of type 'TemplateStringsArray' is not assignable to parameter of type 'Literals'.
  Type 'TemplateStringsArray' is missing the following properties from type 'string[]': pop, push, reverse, shift, and 6 more.ts(2345)

I took a look at the commits were made in overmind-graphql and I see the following change: 576c7de#diff-b00535046c2f50ff11c353cc982bfda7a948198ee6e371dfa81a951ead3876ebL127

You extracted the type

type Literals = string | string[]

from the function

export const gql = (literals: string | readonly string[], ...placeholders: any[]): Query<any, any> => gqlTag(literals, ...placeholders) as any

But you removed readonly keyword (probably because an old version of prettier complains) and it causes the error.

The fix would be to make the type be:

type Literals = string | ReadonlyArray<string>

Then it corresponds to the type from gqlTag, fixes TS error and satisfies eslint/prettier.

Would you mind merging the PR that fixes the issue #527?