[11.x] Fixes validation using shouldConvertToBoolean when parameter uses dot notation

[bytestream]

Given the following validation rules:

['customfield' => ['nullable', 'array'], 'foo' => 'required_if:customfield.1,taylor']

The use of Arr::get() in shouldConvertToBoolean($parameter) results in attributes containing dot notation being parsed. Thus, in the above example, Arr::get($this->rules, 'customfield.1', []) returns array - the second element (zero-indexed) in the customfield validation rules.

The intended behaviour is that it returns all of the validation rules for the customfield.1 attribute.

Without the changes in this PR, the test case fails with the below:

1) Illuminate\Tests\Validation\ValidationValidatorTest::testRequiredIf
TypeError: in_array(): Argument #2 ($haystack) must be of type array, string given

/Users/bytestream/PhpstormProjects/framework/src/Illuminate/Validation/Concerns/ValidatesAttributes.php:2262
/Users/bytestream/PhpstormProjects/framework/src/Illuminate/Validation/Concerns/ValidatesAttributes.php:2243
/Users/bytestream/PhpstormProjects/framework/src/Illuminate/Validation/Concerns/ValidatesAttributes.php:2002
/Users/bytestream/PhpstormProjects/framework/src/Illuminate/Validation/Validator.php:664
/Users/bytestream/PhpstormProjects/framework/src/Illuminate/Validation/Validator.php:459
/Users/bytestream/PhpstormProjects/framework/tests/Validation/ValidationValidatorTest.php:1706