[infra] Support non-cross-compiled ARM64 on Mac testing

The python running on Mac M1 test builders is now native ARM64,
which makes the compilation and test use the xcodebuild/ReleaseARM64
directory, not the xcodebuild/ReleaseXARM64.

Add the xcodebuild/[mode]ARM64 build directories to sharding filesets.

Change-Id: Ide074dab3d4645f1776e83dc62c02f5ded630a9e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/218923
Reviewed-by: Daco Harkes <dacoharkes@google.com>

tools/bots/test_matrix.json

@@ -312,9 +312,11 @@
       "xcodebuild/DebugX64/",
       "xcodebuild/DebugX64C/",
       "xcodebuild/DebugXARM64/",
+      "xcodebuild/DebugARM64/",
       "xcodebuild/ProductX64/",
       "xcodebuild/ProductX64C/",
       "xcodebuild/ProductXARM64/",
+      "xcodebuild/ProductARM64/",
       "xcodebuild/ReleaseIA32/",
       "xcodebuild/ReleaseSIMARM/",
       "xcodebuild/ReleaseSIMARM64/",
@@ -322,6 +324,7 @@
       "xcodebuild/ReleaseX64/",
       "xcodebuild/ReleaseX64C/",
       "xcodebuild/ReleaseXARM64/",
+      "xcodebuild/ReleaseARM64/",
       "pkg/",
       "samples/",
       "samples_2/",