CI test failure: hello cannot find/write log dir

We have a new CI failure concerning the hello test. It's pretty weird, as it concerns the log dir.

```
2021-02-02T17:46:43.2543900Z 1/13 Test #3: hello ............................***Failed 0.16 sec
2021-02-02T17:46:43.2544750Z STDOUT:
2021-02-02T17:46:43.2546240Z STDERR: ERROR: invalid -logdir: cannot find/write /Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/logs
2021-02-02T17:46:43.2547400Z
2021-02-02T17:46:43.2547880Z
2021-02-02T17:46:43.2548550Z CMake Error at runtest.cmake:316 (message):
2021-02-02T17:46:43.2549220Z ***
2021-02-02T17:46:43.2551620Z /Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/bin64/drmemory;-debug;-dr_debug;-dr;/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/dynamorio;-batch;-dr_ops;-dumpcore_mask;-dr_ops;0;-callstack_style;0x27;-no_results_to_stderr;--;/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/tests/hello
2021-02-02T17:46:43.2553740Z has the wrong exit code (1): ERROR: invalid -logdir: cannot find/write
2021-02-02T17:46:43.2555110Z /Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/logs
```

Ref: https://github.com/DynamoRIO/drmemory/pull/2376/checks?check_run_id=1816615166