Fix a BUILD file after #2890. (#2898)

I suspect this is due to the PR testing from an older baseline as we
don't currently use a merge queue.

explorer/common/BUILD

@@ -64,7 +64,7 @@ cc_test(
     srcs = ["set_program_phase_raii_test.cpp"],
     deps = [
         ":trace_stream",
-        "//common:gtest_main",
+        "//testing/util:gtest_main",
         "@com_google_googletest//:gtest",
     ],
 )