ci: pin github actions by hash and update via dependabot

[xopham]

What does this PR do?

• Add dependabot for github actions
• Pin actions by hash

Motivation

Pinning 3rd-party GitHub Actions by commit SHA makes them less vulnerable to compromise of the 3rd party. To avoid outdating and non-verbosity, versions are commented after the SHA and updating via dependabot is introduced that will automatically update the commented version tag as well.

In case of a false commit SHA, this change could break the corresponding workflow. Typically, this does not cause major interruptions, but it can for example affect a release pipeline and require restart causing delays.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.
• For internal contributors, a matching PR should be created to the v2-dev branch and reviewed by @DataDog/apm-go.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-05 14:35:35

Comparing candidate commit 2fb957d in PR branch christoph.hamsen/pin-update-gh-actions with baseline commit e1c213d in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 59 metrics, 0 unstable metrics.

[felixge]

LGTM. Thanks you for identifying the issue, providing a solution, and taking care of reducing future maintenance burden on the engineers working in this repository 🙇.

[datadog-datadog-prod-us1]

Datadog Report

Branch report: christoph.hamsen/pin-update-gh-actions
Commit report: f4e0577
Test service: dd-trace-go

✅ 0 Failed, 5222 Passed, 72 Skipped, 1m 57.76s Total Time