bisect.py: fix TREE environment variable when calling build.py
bisect.py: fix TREE environment variable when calling build.py

The build.py script expects the Git URL to be passed in the TREE
environment variable, or read from the kernel Git repository.  If the
repository doesn't have a remote called "origin", or if this remore
does not correspond to the one the current branch is coming from, then
the git_url is set wrongly in the build meta-data.

Fix this by setting the tree URL with the TREE environment variable
when calling the build.py script.

Signed-off-by: Guillaume Tucker <e7e20b7c30f19d4ca6b81319ef81bf200369d137@collabora.com>

kernelci/lava-ci-staging,kernelci/lava-ci-staging,kernelci/lava-ci-staging