Only trigger CodeQL analysis on the schedule event

[nghialv]

What this PR does / why we need it:

The analysis process of CodeQL is too slow to be run during the push or pull_request events.
So this PR fixed the workflow to only trigger the analysis on the schedule event.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[khanhtc1202]

👏
/lgtm

[pipecd-bot]

Code coverage for golang is 34.06%. This pull request decreases coverage by -0.07%.

File	Function	Base	Head	Diff
pkg/app/api/grpcapi/piped_api.go	PipedAPI.ReportApplicationDeployingStatus	--	0.00%	+0.00%
pkg/app/piped/controller/controller.go	controller.reportApplicationDeployingStatus	--	0.00%	+0.00%
pkg/app/piped/cloudprovider/lambda/function.go	FunctionManifestSpec.validate	80.00%	66.67%	-13.33%

[nghialv]

/approve

[pipecd-bot]

This pull request is APPROVED by nghialv.

Approvers can cancel the approval by writing /approve cancel in a comment. Any additional commits also will change this pull request to be not-approved.