[8.3](backport #32281) [metricbeat] gcp: check for nil metadata

[mergify[bot]]

This is an automatic backport of pull request #32281 done by Mergify.

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:green_heart: Build Succeeded

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• Start Time: 2022-08-24T15:46:59.970+0000

• Duration: 55 min 9 sec

Test stats :test_tube:

Test	Results
Failed	0
Passed	1103
Skipped	87
Total	1190

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[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @gpop63? 🙏

[mergify[bot]]

This pull request is now in conflicts. Could you fix it? 🙏 To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b mergify/bp/8.3/pr-32281 upstream/mergify/bp/8.3/pr-32281
git merge upstream/8.3
git push upstream mergify/bp/8.3/pr-32281

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @gpop63? 🙏

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @gpop63? 🙏

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @gpop63? 🙏

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @gpop63? 🙏