mock: add build tag 'testify_no_objx' to opt-out of objx

Add build tag testify_no_objx to allow to exclude method Mock.TestData()
for avoiding dependency on github.com/stretchr/objx.

Author: dolmen

mock/mock_no_objx.go

@@ -0,0 +1,5 @@
+//go:build testify_no_objx || testify_no_deps
+
+package mock
+
+type testData = struct{}

mock/mock_objx.go

@@ -2,6 +2,8 @@
 // maintenance of downstream forks that remove that dependency.
 // See https://github.com/stretchr/testify/issues/1752
 
+//go:build !testify_no_objx && !testify_no_deps
+
 package mock
 
 import "github.com/stretchr/objx"

mock/mock_objx_test.go

@@ -1,3 +1,5 @@
+//go:build !testify_no_objx && !testify_no_deps
+
 package mock
 
 import (