Drop `git diff` command so it is easier to run CI locally if git checkout is a
worktree. Currently it fails because the directory is not recognized as a git
repository.
The `git diff` command was added recently in #28359 commit
fa07ac48d8 and can be avoided just by teeing the
patch to stdout
It is confusing to treat commands as a single string. This change is
also required to support paths and strings with spaces in them in the
future.
This requires replacing TEST_RUNNER_ENV with a global export, because it
no longer works. See:
```bash
$ export ENV="A=1" && $ENV ls
bash: A=1: command not found...
```
Or in the CI task:
+ DIR_UNIT_TEST_DATA=/ci_container_base/ci/scratch/qa-assets/unit_test_data/
+ LD_LIBRARY_PATH=/ci_container_base/depends/i686-pc-linux-gnu/lib
+ BITCOIND=bitcoin-node make -j10 check VERBOSE=1
/ci_container_base/ci/test/03_test_script.sh: line 166: BITCOIND=bitcoin-node: command not found
https://github.com/bitcoin/bitcoin/pull/28954/checks?check_run_id=19096858944https://cirrus-ci.com/task/6718317604372480
