ci: Reduce use of bash -c

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=19096858944
https://cirrus-ci.com/task/6718317604372480

ci/test/00_setup_env.sh

@@ -46,7 +46,6 @@ export RUN_TIDY=${RUN_TIDY:-false}
 # This is needed because some ci machines have slow CPU or disk, so sanitizers
 # might be slow or a reindex might be waiting on disk IO.
 export TEST_RUNNER_TIMEOUT_FACTOR=${TEST_RUNNER_TIMEOUT_FACTOR:-40}
-export TEST_RUNNER_ENV=${TEST_RUNNER_ENV:-}
 export RUN_FUZZ_TESTS=${RUN_FUZZ_TESTS:-false}
 
 # Randomize test order.