cronet tests: Do not run integration tests on R

CtsNetHttpTestCases were missing a DevSdkIgnoreRule after updating the
min_sdk version to R+ (which made it installable on R where the cronet
classes are not in the bootclasspath.)

Test: atest CtsNetHttpTestCases
Bug: 259632936
Change-Id: I706ff92376227c1759fd6e542066fcff3a7cf052
diff --git a/Cronet/tests/cts/Android.bp b/Cronet/tests/cts/Android.bp
index 44b3364..ce8b2d9 100644
--- a/Cronet/tests/cts/Android.bp
+++ b/Cronet/tests/cts/Android.bp
@@ -37,6 +37,7 @@
         "junit",
         "kotlin-test",
         "mockito-target",
+        "net-tests-utils",
         "truth",
     ],
     libs: [