Fix BUILD targets in dynamic modules (#43362)

Author: yanavlasov

source/extensions/dynamic_modules/sdk/cpp/BUILD

@@ -44,15 +44,3 @@ cc_library(
     visibility = ["//visibility:public"],
     deps = [":sdk"],
 )
-
-# Mock implementations for plugin handle interfaces.
-# Used for testing.
-cc_library(
-    name = "sdk_mocks",
-    hdrs = ["sdk_mocks.h"],
-    visibility = ["//visibility:public"],
-    deps = [
-        ":sdk",
-        "@com_google_googletest//:gtest",
-    ],
-)

test/extensions/dynamic_modules/sdk/cpp/BUILD

@@ -0,0 +1,16 @@
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+licenses(["notice"])  # Apache 2
+
+# Mock implementations for plugin handle interfaces.
+# Used for testing.
+cc_library(
+    name = "sdk_mocks",
+    testonly = 1,
+    hdrs = ["sdk_mocks.h"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//source/extensions/dynamic_modules/sdk/cpp:sdk",
+        "@com_google_googletest//:gtest",
+    ],
+)