Move testing.go to srcs from testSrcs.

This is needed so that tests in other packages can depend on it.

Bug: 232520859
Test: Manually run m nothing to verify that all tests passed
Change-Id: Ief64e8d0e4030431b26cb5526c9f8beab94cad23

bp2build/Android.bp

@@ -15,6 +15,7 @@ bootstrap_go_package {
         "conversion.go",
         "metrics.go",
         "symlink_forest.go",
+        "testing.go",
     ],
     deps: [
         "soong-android",
@@ -68,7 +69,6 @@ bootstrap_go_package {
         "python_library_conversion_test.go",
         "sh_conversion_test.go",
         "soong_config_module_type_conversion_test.go",
-        "testing.go",
     ],
     pluginFor: [
         "soong_build",