Read shell's PATH rather than make's to avoid warning logspam.

This applies the same change to AOSP's robolectric 3.1.1 as
what another change with the same Change-Id already applied
to internal versions of robolectric.

Bug: 70518982
Test: Visual inspection of the change only. Ran test at
      subsequent CL.
Change-Id: I491fede7f0a64e1da4e63052802fd153a8b76d3f
Merged-In: I491fede7f0a64e1da4e63052802fd153a8b76d3f
diff --git a/common/robolectric/robotest-internal.mk b/common/robolectric/robotest-internal.mk
index 9a716cb..4ad2ec5 100644
--- a/common/robolectric/robotest-internal.mk
+++ b/common/robolectric/robotest-internal.mk
@@ -49,7 +49,7 @@
 	  PRIVATE_TARGET_MESSAGE="$(PRIVATE_TARGET_MESSAGE)" \
 	  PRIVATE_TIMEOUT="$(PRIVATE_TIMEOUT)" \
 	  PRIVATE_TESTS="$(PRIVATE_TESTS)" \
-	  PATH=${ANDROID_JAVA8_HOME}/bin:${PATH} \
+	  PATH=${ANDROID_JAVA8_HOME}/bin:$${PATH} \
 	  $(PRIVATE_ROBOLECTRIC_SCRIPT_PATH)/wrapper.sh \
 	    "$(PRIVATE_MODULE)" \
 	    "$(PRIVATE_TARGET_OUTPUT)" \