[8.15](backport #5196) [pkg][fix] - Filter non-fatal errors and update go.mod

[mergify]

What does this PR do?

With elastic/elastic-agent-system-metrics#164, we now also expect a list of non-fatal errors (access denied, operation not permitted, invalid parameters etc).
Such errors are safe to ignore, so update the tests
Also,

• update go.mod

Why is it important?

Checklist

• My code follows the style guidelines of this project
• 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
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

Related issues

• See [system/process] add support for mutlierr  elastic-agent-system-metrics#172 for information around non-fatal errros.

---

This is an automatic backport of pull request #5196 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of a1fd2c9 has failed:

On branch mergify/bp/8.15/pr-5196
Your branch is up to date with 'origin/8.15'.

You are currently cherry-picking commit a1fd2c9d9a.
  (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:   pkg/testing/fixture_install.go
	modified:   pkg/utils/watcher.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   NOTICE.txt
	both modified:   go.mod
	both modified:   go.sum

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

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)