[BUG] Exception hit during verify_github_token: The token is not yet valid (iat)

## Vault server version
v1.14.1

## vault-action version
v2.7.4

## Describe the bug
We ran into a scenario where we believe clock drift between the github runner and the vault server were out of sync; specifically the runner being ahead of the vault. This resulted in authentication failures.

## To Reproduce
Set the issued at (IAT) to a time farther in the future.

## Expected behavior
Error free authentication.

## Log Output
Exception hit during verify_github_token: The token is not yet valid (iat)

## Additional context
Github recommends setting the issued at (iat) to 60 seconds in the past to better handle this scenario, however the action currently uses now().

https://docs.github.com/en/enterprise-server@3.12/apps/creating-github-apps/authenticating-with-a-github-app/generating-a-json-web-token-jwt-for-a-github-app

For our Hashi friends, please reference ticket 144645 since we weren't able to have a deeper conversation around https://developer.hashicorp.com/vault/api-docs/auth/jwt#clock_skew_leeway.

Start at the verify_github_token authentication path identified in the log and compare its issued-at handling with GitHub's JWT guidance linked in the issue. Done means authentication remains error-free when the runner clock is ahead of Vault within the described drift scenario, while preserving normal token verification.

Written by the indexing model from the issue text.