rust_uprev: mark test_success_with_template mock_find_ebuild unused

Pre-submit checks complained that the mock_find_ebuild parameter to
test_success_with_template is unused. This change avoids the warning
by prefixing the paramter name with an underscore to indicate that
it is unused.

BUG=None
TEST=python3 ./rust_tools/rust_uprev_test.py

Change-Id: Ieadd3854970a1662a74159fd9e492d6ee2f5f963
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2593513
Tested-by: Bob Haarman <inglorion@chromium.org>
Reviewed-by: Tiancong Wang <tcwang@google.com>
Commit-Queue: Bob Haarman <inglorion@chromium.org>
diff --git a/rust_tools/rust_uprev_test.py b/rust_tools/rust_uprev_test.py
index fc50600..0de785e 100755
--- a/rust_tools/rust_uprev_test.py
+++ b/rust_tools/rust_uprev_test.py
@@ -57,7 +57,7 @@
       'find_ebuild_for_rust_version',
       return_value='/path/to/ebuild')
   @mock.patch.object(rust_uprev, 'get_command_output')
-  def test_success_with_template(self, mock_command, mock_find_ebuild):
+  def test_success_with_template(self, mock_command, _mock_find_ebuild):
     expected = (self.version_old, '/path/to/ebuild')
     actual = rust_uprev.prepare_uprev(
         rust_version=self.version_new, template=self.version_old)