build: Fix path to openapi-gen binary (#5089)

Signed-off-by: terrytangyuan <terrytangyuan@gmail.com>

Makefile

@@ -106,11 +106,11 @@ define protoc
       -I /usr/local/include \
       -I $(CURDIR) \
       -I $(CURDIR)/vendor \
-      -I ${GOPATH}/src \
-      -I ${GOPATH}/pkg/mod/github.com/gogo/protobuf@v1.3.1/gogoproto \
-      -I ${GOPATH}/pkg/mod/github.com/grpc-ecosystem/grpc-gateway@v1.16.0/third_party/googleapis \
-      --gogofast_out=plugins=grpc:${GOPATH}/src \
-      --grpc-gateway_out=logtostderr=true:${GOPATH}/src \
+      -I $(GOPATH)/src \
+      -I $(GOPATH)/pkg/mod/github.com/gogo/protobuf@v1.3.1/gogoproto \
+      -I $(GOPATH)/pkg/mod/github.com/grpc-ecosystem/grpc-gateway@v1.16.0/third_party/googleapis \
+      --gogofast_out=plugins=grpc:$(GOPATH)/src \
+      --grpc-gateway_out=logtostderr=true:$(GOPATH)/src \
       --swagger_out=logtostderr=true,fqn_for_swagger_name=true:. \
       $(1)
      perl -i -pe 's|argoproj/argo-workflows/|argoproj/argo-workflows/v3/|g' `echo "$(1)" | sed 's/proto/pb.go/g'`
@@ -298,7 +298,7 @@ $(GOPATH)/bin/goimports:
 pkg/apis/workflow/v1alpha1/generated.proto: $(GOPATH)/bin/go-to-protobuf $(PROTO_BINARIES) $(TYPES)
 	go mod vendor
 	[ -e v3 ] || ln -s . v3
-	${GOPATH}/bin/go-to-protobuf \
+	$(GOPATH)/bin/go-to-protobuf \
 		--go-header-file=./hack/custom-boilerplate.go.txt \
 		--packages=github.com/argoproj/argo-workflows/v3/pkg/apis/workflow/v1alpha1 \
 		--apimachinery-packages=+k8s.io/apimachinery/pkg/util/intstr,+k8s.io/apimachinery/pkg/api/resource,k8s.io/apimachinery/pkg/runtime/schema,+k8s.io/apimachinery/pkg/runtime,k8s.io/apimachinery/pkg/apis/meta/v1,k8s.io/api/core/v1,k8s.io/api/policy/v1beta1 \
@@ -498,7 +498,7 @@ clean:
 
 pkg/apis/workflow/v1alpha1/openapi_generated.go: $(GOPATH)/bin/openapi-gen $(TYPES)
 	[ -e v3 ] || ln -s . v3
-	openapi-gen \
+	$(GOPATH)/bin/openapi-gen \
 	  --go-header-file ./hack/custom-boilerplate.go.txt \
 	  --input-dirs github.com/argoproj/argo-workflows/v3/pkg/apis/workflow/v1alpha1 \
 	  --output-package github.com/argoproj/argo-workflows/v3/pkg/apis/workflow/v1alpha1 \
@@ -509,7 +509,7 @@ pkg/apis/workflow/v1alpha1/openapi_generated.go: $(GOPATH)/bin/openapi-gen $(TYP
 # generates many other files (listers, informers, client etc).
 pkg/apis/workflow/v1alpha1/zz_generated.deepcopy.go: $(TYPES)
 	[ -e v3 ] || ln -s . v3
-	bash ${GOPATH}/pkg/mod/k8s.io/code-generator@v0.19.6/generate-groups.sh \
+	bash $(GOPATH)/pkg/mod/k8s.io/code-generator@v0.19.6/generate-groups.sh \
 		"deepcopy,client,informer,lister" \
 		github.com/argoproj/argo-workflows/v3/pkg/client github.com/argoproj/argo-workflows/v3/pkg/apis \
 		workflow:v1alpha1 \