fix: eslint rule to suppress bogus dependency warning

[erights]

In keybase @katelynsills said:

Btw, the way to turn off the annoying red squigglies in tests when they tell you something you import should be a real dependency is this ESLint setting:

"import/no-extraneous-dependencies": [
        "error",
        {
          "devDependencies": true
        }
      ]

This PR does that.

[katelynsills]

LGTM!