[BUG] Changlog is not updated by 'Dependabot PR actions' workflow when initially created for Dependabot PRs

[tlfeng]

Describe the bug Please see https://github.com/opensearch-project/OpenSearch/pull/4547#issuecomment-1251875724

When dependabot PRs are initially created, the GHA workflow 'Dependabot PR actions' (https://github.com/opensearch-project/OpenSearch/blob/2.3.0/.github/workflows/dependabot_pr.yml#L51) will not update the changelog file. Only ask dependabot to "recreate" the PR can solve the problem.

All the PRs created by dependabot on yesterday have got the problem: https://github.com/opensearch-project/OpenSearch/pulls?q=is%3Apr+label%3Adependabot+created%3A2022-09-19

To Reproduce Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior A clear and concise description of what you expected to happen.

Plugins Please list all plugins currently enabled.

Screenshots If applicable, add screenshots to help explain your problem.

Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context Add any other context about the problem here.