fix(github-workflows): use official GitHub action for token generation

[bthuilot]

What does this PR do?

• Replaces usage of tibdex/github-app-token with official GitHub action

[bthuilot]

Dismissing "pin by tag" due to sensitivity of action and lack of dependabot

[datadog-datadog-prod-us1]

🟠 Code Vulnerability

Workflow depends on a GitHub actions pinned by tag (...read more)

When using a third party action, one needs to provide its GitHub path (owner/project) and can eventually pin it to a Git ref (a branch name, a Git tag, or a commit hash).

No pinned Git ref means the action uses the latest commit of the default branch each time it runs, eventually running newer versions of the code that were not audited by Datadog. Specifying a Git tag is better, but since they are not immutable, using a full length hash is recommended to make sure the action content is actually frozen to some reviewed state.

Be careful however, as even pinning an action by hash can be circumvented by attackers still. For instance, if an action relies on a Docker image which is itself not pinned to a digest, it becomes possible to alter its behaviour through the Docker image without actually changing its hash. You can learn more about this kind of attacks in Unpinnable Actions: How Malicious Code Can Sneak into Your GitHub Actions Workflows. Pinning actions by hash is still a good first line of defense against supply chain attacks.

Additionally, pinning by hash or tag means the action won’t benefit from newer version updates if any, including eventual security patches. Make sure to regularly check if newer versions for an action you use are available. For actions coming from a very trustworthy source, it can make sense to use a laxer pinning policy to benefit from updates as soon as possible.