Firefox 138 beta adds script importmap integrity (#26513)

added version added for importmap.integrity for firefox

Author: dletorey

html/elements/script.json

@@ -651,7 +651,7 @@
                   "chrome_android": "mirror",
                   "edge": "mirror",
                   "firefox": {
-                    "version_added": false
+                    "version_added": "138"
                   },
                   "firefox_android": "mirror",
                   "ie": {