[8.19](backport #4891) Update to go 1.24.3

[mergify]

What is the problem this PR solves?

This PR updates the Go language version used in the project from 1.24.1 to 1.24.2 across all relevant modules (go.mod, dev-tools/go.mod, testing/go.mod).
Keeping the Go version up to date ensures we benefit from the latest bug fixes, performance improvements, and security patches.

Depends on:

• Revert "Remove context.background and variable copy from test case" #4892

How does this PR solve the problem?

The CI configuration (.ci/bump-golang.yml) was adjusted to correctly detect and update Go versions in all relevant go.mod files.
The go.mod files for the main project, dev tools, and testing were updated to reference Go 1.24.2.
A changelog fragment was added to document this upgrade.

How to test this PR locally

N/A

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

Related issues

N/A

---

This is an automatic backport of pull request #4891 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 9dd0054 has failed:

On branch mergify/bp/8.19/pr-4891
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit 9dd0054.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .ci/bump-golang.yml
	new file:   changelog/fragments/1746596216-Update-to-go-1.24.3.yaml

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   dev-tools/go.mod
	both modified:   go.mod
	both modified:   testing/go.mod

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[prodsecmachine]

🎉 Snyk checks have passed. No issues have been found so far.

✅ security/snyk check is complete. No issues have been found. (View Details)

✅ license/snyk check is complete. No issues have been found. (View Details)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube