refctor: replace indexOf with strict equality (#864)

* refctor: replace startsWith with strict equality

* chore: revert

* chore: revert

* Create serious-plants-decide.md

---------

Co-authored-by: Yosuke Ota <[email protected]>

Author: btea

.changeset/serious-plants-decide.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-regexp": minor
+---
+
+refctor: replace `indexOf()` with strict equality

lib/rules/sort-character-class-elements.ts

@@ -302,7 +302,7 @@ function escapeRaw(node: CharacterClassElement, target: CharacterClassElement) {
             | UnicodeSetsCharacterClassElement
             | ClassRangesCharacterClassElement
         )[] = parent.elements
-        if (elements.indexOf(target) === 0) {
+        if (elements[0] === target) {
             raw = `\\${raw}`
         }
     }