docs: update to eslint v9 in custom-rule-tutorial

[aladdin-add]

fixes #18382

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[ ] Bug fix (template)
[ ] New rule (template)
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[ ] Add autofix to a rule
[ ] Add a CLI option
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[mdjermanovic]

We should update the same in the example project that is linked from the tutorial:

eslint/docs/_examples/custom-rule-tutorial-code/enforce-foo-bar.test.js

Lines 10 to 14 in b4d2512

	const ruleTester = new RuleTester({
	// Must use at least ecmaVersion 2015 because
	// that's when `const` variable were introduced.
	parserOptions: { ecmaVersion: 2015 }
	});

[mdjermanovic]

We should probably also update all references to ESLint v8 (e.g, devDependencies, peerDependencies) to ESLint v9.

[aladdin-add]

005ee25

[aladdin-add]

I also added this property - to avoid it being published unexpectedly.

[mdjermanovic]

Few more places to update to v9:

eslint/docs/src/extend/custom-rule-tutorial.md

Line 365 in 005ee25

1. `"peerDependencies"`: Add `"eslint": ">=8.0.0"` as a peer dependency. Any version greater than or equal to that is necessary to use the plugin. Declaring `eslint` as a peer dependency requires that users add the package to the project separately from the plugin.

eslint/docs/src/extend/custom-rule-tutorial.md

Lines 382 to 385 in 005ee25

	// Add eslint>=8.0.0 as a peer dependency.
	"peerDependencies": {
	"eslint": ">=8.0.0"
	},

eslint/docs/src/extend/custom-rule-tutorial.md

Lines 394 to 396 in 005ee25

	"devDependencies": {
	"eslint": "^8.36.0"
	}

[mdjermanovic]

LGTM, thanks!