test: make sure workflow_call is not a github event calling our workflow

[KnisterPeter]

Since reusable workflows are defining inputs and ouputs using the
on.workflow_call syntax, this could also be triggered by a workflow_call
event. That event does not exist within GitHub and we should make
sure our worklow is not called by that kind of 'synthetic' event.

See https://github.com/nektos/act/pull/1423/files/74da5b085c0c4d08c5e5bf53501e555cb585b26c#r1042413431

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ REPOSITORY	gitleaks	yes		no	2.79s
✅ REPOSITORY	git_diff	yes		no	0.0s
✅ REPOSITORY	secretlint	yes		no	1.11s

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Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff

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[codecov]

Codecov Report

Merging #1520 (c956d2d) into master (4989f44) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1520      +/-   ##
==========================================
+ Coverage   61.22%   61.26%   +0.04%     
==========================================
  Files          46       46              
  Lines        7141     7149       +8     
==========================================
+ Hits         4372     4380       +8     
  Misses       2462     2462              
  Partials      307      307              

Impacted Files	Coverage Δ
pkg/runner/job_executor.go	88.40% <100.00%> (+0.71%)	⬆️

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