GitHub.DistributedTask.ObjectTemplating.TemplateValidationException: The template is not valid. /home/runner/work/ci-imgs/ci-imgs/./.github/actions/compute-matrix/action.yml (Line: 21, Col: 7): Required property is missing: shell
at GitHub.DistributedTask.ObjectTemplating.TemplateValidationErrors.Check()
at GitHub.Runner.Worker.ActionManifestManager.ConvertRuns(IExecutionContext executionContext, TemplateContext templateContext, TemplateToken inputsToken, String fileRelativePath, MappingToken outputs)
at GitHub.Runner.Worker.ActionManifestManager.Load(IExecutionContext executionContext, String manifestFile)