hcl2template/common_test.go: make testParse a helper (#8495)
hcl2template/common_test.go: make testParse a helper (#8495)

so that when an error happens we see the real calling function
dave2/packer,hashicorp/packer,dave2/packer,mitchellh/packer,dave2/packer,grubernaut/packer,mitchellh/packer,paulmey/packer,ricardclau/packer,paulmey/packer,pecigonzalo/packer,mitchellh/packer,ricardclau/packer,ricardclau/packer,paulmey/packer,pecigonzalo/packer,ricardclau/packer,mitchellh/packer,dave2/packer,ricardclau/packer,grubernaut/packer,paulmey/packer,rnaveiras/packer,rnaveiras/packer,paulmey/packer,rnaveiras/packer,grubernaut/packer,rnaveiras/packer,dave2/packer,paulmey/packer,grubernaut/packer,rnaveiras/packer,hashicorp/packer,dave2/packer,grubernaut/packer,grubernaut/packer,ricardclau/packer,pecigonzalo/packer,rnaveiras/packer,mitchellh/packer,hashicorp/packer,pecigonzalo/packer,hashicorp/packer