fix(deps): update dependency @google-cloud/iot to v3 (#576)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [@google-cloud/iot](https://github.com/googleapis/nodejs-iot) | [`^2.0.0` -> `^3.0.0`](https://renovatebot.com/diffs/npm/@google-cloud%2fiot/2.5.1/3.1.0) | [![age](https://badges.renovateapi.com/packages/npm/@google-cloud%2fiot/3.1.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/npm/@google-cloud%2fiot/3.1.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/npm/@google-cloud%2fiot/3.1.0/compatibility-slim/2.5.1)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/npm/@google-cloud%2fiot/3.1.0/confidence-slim/2.5.1)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>googleapis/nodejs-iot</summary>

### [`v3.1.0`](https://github.com/googleapis/nodejs-iot/blob/HEAD/CHANGELOG.md#&#8203;310-httpsgithubcomgoogleapisnodejs-iotcomparev300v310-2022-07-05)

[Compare Source](https://github.com/googleapis/nodejs-iot/compare/v2.5.1...v3.1.0)

##### Features

-   support regapic LRO ([b02cd4d](https://github.com/googleapis/nodejs-iot/commit/b02cd4d8f954fa1c34ef77055eb5c0b628095482))

</details>

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samples/access_token_example/package.json

@@ -19,7 +19,7 @@
     "test": "mocha --timeout=600000"
   },
   "dependencies": {
-    "@google-cloud/iot": "^2.0.0",
+    "@google-cloud/iot": "^3.0.0",
     "@google-cloud/pubsub": "^3.0.0",
     "@google-cloud/storage": "^6.0.0",
     "yargs": "^16.0.0",

samples/manager/package.json

@@ -19,7 +19,7 @@
     "test": "mocha --timeout=600000"
   },
   "dependencies": {
-    "@google-cloud/iot": "^2.0.0",
+    "@google-cloud/iot": "^3.0.0",
     "@google-cloud/pubsub": "^3.0.0",
     "yargs": "^16.0.0"
   },

samples/mqtt_example/package.json

@@ -19,7 +19,7 @@
     "test": "mocha --timeout=600000"
   },
   "dependencies": {
-    "@google-cloud/iot": "^2.0.0",
+    "@google-cloud/iot": "^3.0.0",
     "@google-cloud/pubsub": "^3.0.0",
     "jsonwebtoken": "^8.5.0",
     "mqtt": "^4.0.0",