Replace deprecated rule (#305)

Replace `scss/at-import-partial-extension` with `scss/load-partial-extension` introduced with `stylelint-scss` 6.4.0

index.js

@@ -20,14 +20,14 @@ module.exports = {
 		],
 		'scss/at-extend-no-missing-placeholder': true,
 		'scss/at-if-no-null': true,
-		'scss/at-import-partial-extension': 'never',
 		'scss/at-rule-no-unknown': true,
 		'scss/comment-no-empty': true,
 		'scss/declaration-nested-properties-no-divided-groups': true,
 		'scss/dollar-variable-no-missing-interpolation': true,
 		'scss/function-quote-no-quoted-strings-inside': true,
 		'scss/function-unquote-no-unquoted-strings-inside': true,
 		'scss/load-no-partial-leading-underscore': true,
+		'scss/load-partial-extension': 'never',
 		'scss/no-duplicate-mixins': true,
 		'scss/no-global-function-names': true,
 		'scss/operator-no-newline-after': true,