fix(ci): address conditional type on_merge

Author: heitorlessa

.github/scripts/constants.js

@@ -15,8 +15,8 @@ module.exports = Object.freeze({
     /** @type {number} */
     "PR_NUMBER": process.env.PR_NUMBER || 0,
 
-    /** @type {boolean} */
-    "PR_IS_MERGED": process.env.PR_IS_MERGED || false,
+    /** @type {string} */
+    "PR_IS_MERGED": process.env.PR_IS_MERGED || "false",
 
     /** @type {string} */
     "LABEL_BLOCK": "do-not-merge",

.github/scripts/label_related_issue.js

@@ -13,7 +13,7 @@ module.exports = async ({github, context, core}) => {
       return core.notice("Author in IGNORE_AUTHORS list; skipping...")
     }
 
-    if (!PR_IS_MERGED) {
+    if (PR_IS_MERGED == "false") {
       return core.notice("Only merged PRs to avoid spam; skipping")
     }