fix: ignore yml files inside node_modules dir

[vigneshshanmugam]

• fix validation with node_modules monitor examples #712
• Ignores all the yaml files inside node_modules and .github directory to be defensive from adding the monitors that are added as templates from the Elastic synthetics source package itself.

[apmmachine]

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• Start Time: 2023-03-09T20:45:40.300+0000

• Duration: 15 min 57 sec

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Total	215

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[dominiqueclarke]

LGTM. Tested by duplicating my existing heartbeat.yml file in node_modules for the project. Was able to recreate the issue and confirm it's fixed by this PR.