Pull out .#isBoosted() in rollup-controller

app/javascript/controllers/rollup_controller.js

@@ -8,7 +8,7 @@ export default class extends Controller {
   }
 
   #summarizeBoosts() {
-    if (this.hasBoostEventTarget) {
+    if (this.#isBoosted) {
       const el = document.createElement("span")
       el.dataset.turboTemporary = ""
       el.textContent = this.#boostSumaries.toSentence()
@@ -16,6 +16,10 @@ export default class extends Controller {
     }
   }
 
+  get #isBoosted() {
+    return this.hasBoostEventTarget
+  }
+
   get #boostSumaries() {
     return Object.entries(this.#boostsByCreator).map(([_creatorId, boostEvents]) => {
       return `${boostEvents[0].dataset.creatorName} +${boostEvents.length}`