tests: clean up repo_trace._TRACE_FILE patching

Patch this automatically for all tests rather than duplicating the
boilerplate in diff testcases.

Change-Id: I391d5c859974cda3d5680d34ede2ce6e9e925838
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/354358
Reviewed-by: Joanna Wang <jojwang@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

tests/conftest.py

@@ -0,0 +1,25 @@
+# Copyright 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Common fixtures for pytests."""
+
+import pytest
+
+import repo_trace
+
+
+@pytest.fixture(autouse=True)
+def disable_repo_trace(tmp_path):
+  """Set an environment marker to relax certain strict checks for test code."""
+  repo_trace._TRACE_FILE = str(tmp_path / 'TRACE_FILE_from_test')