Bump webextension-polyfill in /samples/web-extension/javascript

Bumps [webextension-polyfill](https://github.com/mozilla/webextension-polyfill) from 0.7.0 to 0.8.0.
- [Release notes](https://github.com/mozilla/webextension-polyfill/releases)
- [Commits](mozilla/webextension-polyfill@0.7.0...0.8.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

samples/web-extension/javascript/package-lock.json

@@ -13,7 +13,7 @@
   "author": "The Glean Team <glean-team@mozilla.com>",
   "license": "MPL-2.0",
   "dependencies": {
-    "webextension-polyfill": "^0.7.0"
+    "webextension-polyfill": "^0.8.0"
   },
   "devDependencies": {
     "mocha": "^8.3.2",