fix: data race on count pending Falco events

[dwisiswant0]

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Summary

Race condition while count pending Falco events in checkFalcoEvents.

Proposed of changes

This PR fixes/implements the following bugs/features:

• 111

How has this been tested?

Proof:

$ go test -v -cover -race -count=1 -run="TestNewWithFalcoSidekickURL" ./
=== RUN   TestNewWithFalcoSidekickURL
--- PASS: TestNewWithFalcoSidekickURL (8.19s)
PASS
coverage: 48.2% of statements
ok      github.com/kitabisa/teler-waf   9.243s  coverage: 48.2% of statements

Closing issues

Fixe #111

Checklist:

• [x] My code follows the code style of this project.
• [x] My changes successfully ran and pass linters locally (run make lint).
• [x] I have written new tests for my changes.
  • [x] My changes successfully ran and pass tests locally.
• [ ] My change requires a change to the documentation.
  • [ ] I have updated the documentation accordingly.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (2914f61) 76.81% compared to head (78d7003) 78.60%. Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #112 +/- ## ========================================== + Coverage 76.81% 78.60% +1.78% ========================================== Files 6 6 Lines 1113 1117 +4 ========================================== + Hits 855 878 +23 + Misses 206 187 -19 Partials 52 52 ``` | [Files](https://app.codecov.io/gh/kitabisa/teler-waf/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=kitabisa) | Coverage Δ | | |---|---|---| | [falcosidekick.go](https://app.codecov.io/gh/kitabisa/teler-waf/pull/112?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=kitabisa#diff-ZmFsY29zaWRla2ljay5nbw==) | `54.23% <75.00%> (+37.87%)` | :arrow_up: |

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