Fix tests failing in CI for Auditbeat x-pack in OSX

[jsoriano]

While trying to add some missing stages for Auditbeat x-pack in Jenkins (#18835), some tests were failing:

• A check in the homebrew test for the package dataset

package_homebrew_test.go:74: 
Error Trace:	package_homebrew_test.go:74
            				package_homebrew_test.go:61
Error:      	Not equal: 
            	expected: "Krm421rtYM4wgq1S"
            	actual  : "cPZnKnE1DL7pmz7t"
            	
            	Diff:
            	--- Expected
            	+++ Actual
            	@@ -1 +1 @@
            	-Krm421rtYM4wgq1S
            	+cPZnKnE1DL7pmz7t
Test:       	TestHomebrew

• Same module, in TestData ([Auditbeat] Error from system/package dataset on darwin at startup #18536):

package_test.go:29: received error: gob: type not registered for interface: errors.withStack
    error encoding packages
    github.com/elastic/beats/v7/x-pack/auditbeat/module/system/package.(*MetricSet).savePackagesToDisk
/private/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/src/github.com/elastic/beats/x-pack/auditbeat/module/system/package/package.go:466
    github.com/elastic/beats/v7/x-pack/auditbeat/module/system/package.(*MetricSet).reportState
/private/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/src/github.com/elastic/beats/x-pack/auditbeat/module/system/package/package.go:313
    github.com/elastic/beats/v7/x-pack/auditbeat/module/system/package.(*MetricSet).Fetch
/private/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/src/github.com/elastic/beats/x-pack/auditbeat/module/system/package/package.go:266
    github.com/elastic/beats/v7/metricbeat/mb/testing.ReportingFetchV2
/private/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/src/github.com/elastic/beats/metricbeat/mb/testing/modules.go:254
    github.com/elastic/beats/v7/x-pack/auditbeat/module/system/package.TestData
/private/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/src/github.com/elastic/beats/x-pack/auditbeat/module/system/package/package_test.go:27
    testing.tRunner
/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/.gvm/versions/go1.13.10.darwin.amd64/src/testing/testing.go:909
    runtime.goexit
/var/lib/jenkins/workspace/Beats_beats-beats-mbp_PR-18835/.gvm/versions/go1.13.10.darwin.amd64/src/runtime/asm_amd64.s:1357

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[andrewkroh]

Relates #18536

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.