Upgrade action to use node20 (#121)

* Action update:

- Bump all dependencies
- Rewrite `getLatestHelmVersion()` function without graphql

* Bump stableHelmVersion

* Update readme and action.yaml

* Revert and rewrite with @octokit/action

* Add latest to integration test

* Bump action's versions

* Set github.token as default input

* Replace deprecated jest methods

* Add prettier to dev dependencies, fix prettier issues

action.yml

@@ -8,6 +8,7 @@ inputs:
    token:
       description: GitHub token. Required only if 'version' == 'latest'
       required: false
+      default: '${{ github.token }}'
    downloadBaseURL:
       description: 'Set the download base URL'
       required: false
@@ -18,5 +19,5 @@ outputs:
 branding:
    color: 'blue'
 runs:
-   using: 'node16'
+   using: 'node20'
    main: 'lib/index.js'