Revert test_source changes.

Closes https://github.com/dart-lang/dart_ci/pull/169

GitOrigin-RevId: 41e8d16f54afbb27eff7ce310a725765ef4712c5
Change-Id: I27d8200487cb170129c14d81a7f37ada9d497a13
Reviewed-on: https://dart-review.googlesource.com/c/dart_ci/+/417640
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>
diff --git a/appengine/lib/src/test_source.dart b/appengine/lib/src/test_source.dart
index 88cbe94..008f531 100644
--- a/appengine/lib/src/test_source.dart
+++ b/appengine/lib/src/test_source.dart
@@ -167,7 +167,7 @@
   String root;
   if (isCo19(suite)) {
     revision = await findDepsRevision(revision, suite);
-    root = "https://github.com/dart-lang/co19/blob/master/$revision/";
+    root = "https://github.com/dart-lang/co19/blob/$revision/";
   } else if (isExternalPackage(suite)) {
     final package = parts.first;
     revision = await findDepsRevision(revision, package);
@@ -176,7 +176,7 @@
   } else {
     root = useGob
         ? "https://dart.googlesource.com/sdk/+/$revision/"
-        : "https://github.com/dart-lang/sdk/blob/main/$revision/";
+        : "https://github.com/dart-lang/sdk/blob/$revision/";
   }
   return findTestFile(testName, Uri.parse(root), suite, parts);
 }