bisect-kit: fix a bug in PatchGitConfig
The returned object of the context manager is to be used as a dict like
```
with PatchGitConfig() as new_env:
if 'env' in kwargs:
new_env = kwargs['env'] | new_env
```
If __enter__ return None, the | operator would fail
```
TypeError: unsupported operand type(s) for |: 'dict' and 'NoneType'
```
BUG=b:320187111
TEST=manual && run_formatter.sh && run_test.sh
Change-Id: I50a896f1607693055755bbf0edb13d5125b5049a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/bisect-kit/+/5369293
Reviewed-by: MD Nayeem Jahan Rafi <njrafi@chromium.org>
Commit-Queue: Cheng-Yu Lee <cylee@google.com>
Tested-by: Cheng-Yu Lee <cylee@google.com>
1 file changed
