fix(types): allow files options to be simple strings as well as arrays

Originally, these files options just accepted strings, but they were
modified to accept arrays of strings too whilst we were adding
lint-staged support so that that plugin could pass in an array of globs.
We allowed single strings to still be set as options in order to
preserve backwards compatibility, but when writing the original schemas
for the migration script the option was encoded as a string array
because we planned to deprecate a single string option eventually so it
made sense for the migration script to only offer new users to create a
list of file globs. However, this became a problem when we translated
that schema into a zod schema that would also be used to validate the
options a user has set, as that original schema did not allow single
strings. This inadvertently created a breaking change when moving to
zod.

To work around this breaking change, let's tell zod that either a string
or an array of strings is valid. We can roll this back in a future major
version if we wish.

lib/types/src/schema/eslint.ts

@@ -1,7 +1,7 @@
 import { z } from 'zod'
 
 export const ESLintSchema = z.object({
-  files: z.string().array().default(['**/*.js']),
+  files: z.string().array().or(z.string()).default(['**/*.js']),
   config: z.record(z.unknown()).optional(), // @deprecated: use options instead
   options: z.record(z.unknown()).optional()
 })

lib/types/src/schema/prettier.ts

@@ -1,7 +1,7 @@
 import { z } from 'zod'
 
 export const PrettierSchema = z.object({
-  files: z.string().array().default(['**/*.{js,jsx,ts,tsx}']),
+  files: z.string().array().or(z.string()).default(['**/*.{js,jsx,ts,tsx}']),
   configFile: z.string().optional(),
   ignoreFile: z.string().default('.prettierignore'),
   configOptions: z.record(z.unknown()).default({