Do not log error if sync variable is not set (#1466)

[tbavelier]

What does this PR do?

Cherry-pick 427385c from #1466

Motivation

Refer to original PR, uncovered during QA

Additional Notes

Anything else we should know when reviewing?

Minimum Agent Versions

Are there minimum versions of the Datadog Agent and/or Cluster Agent required?

• Agent: vX.Y.Z
• Cluster Agent: vX.Y.Z

Describe your test plan

• Refer to [DatadogMonitor] Do not log error if DD_MONITOR_FORCE_SYNC_PERIOD is not set #1466

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 49.20%. Comparing base (648b7c7) to head (ae63fde).

Files with missing lines	Patch %	Lines
internal/controller/datadogmonitor/controller.go	11.11%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            v1.10    #1469      +/-   ##
==========================================
- Coverage   49.22%   49.20%   -0.02%     
==========================================
  Files         224      224              
  Lines       19700    19701       +1     
==========================================
- Hits         9697     9694       -3     
- Misses       9497     9501       +4     
  Partials      506      506              

Flag	Coverage Δ
unittests	49.20% <11.11%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
internal/controller/datadogmonitor/controller.go	46.69% <11.11%> (-1.36%)	⬇️

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[tbavelier]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in v1.10 is 0s.

Use /merge -c to cancel this operation!