[8.3](backport #700) Fix for the filebeat spec file picking up packetbeat inputs

[mergify]

This is an automatic backport of pull request #700 done by Mergify.
Cherry-pick of 4dcc16b has failed:

On branch mergify/bp/8.3/pr-700
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Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   internal/pkg/agent/program/testdata/single_config-packetbeat.yml
	modified:   internal/pkg/agent/program/testdata/single_config.yml
	modified:   internal/spec/filebeat.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   internal/pkg/agent/program/supported.go

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

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	97.222% (70/72)	👍
Files	68.636% (151/220)	👍
Classes	68.254% (301/441)	👍
Methods	51.722% (826/1597)	👍
Lines	38.027% (8858/23294)	👎 -0.017
Conditionals	100.0% (0/0)	💚