CI fails with macos build, even with no code changes

[edwardhartnett]

This is happening with #2964, which has documentation changes only. So all builds should always work. Yet on MacOS there are failures:

73: Test command: /bin/bash "-c" "export srcdir=/Users/runner/work/netcdf-c/netcdf-c/nc_test4;export TOPSRCDIR=/Users/runner/work/netcdf-c/netcdf-c;/Users/runner/work/netcdf-c/netcdf-c/build/nc_test4/test_fillonly.sh "
73: Working Directory: /Users/runner/work/netcdf-c/netcdf-c/build/nc_test4
73: Test timeout computed to be: 1500
36: *** SUCCEED: ref_tst_long_charconst
21: No such file or directory
21: Location: file /Users/runner/work/netcdf-c/netcdf-c/ncdump/nccopy.c; fcn copy line 2010
 62/203 Test  #21: ncdump_tst_nccopy3 ....................***Failed    0.39 sec

[WardF]

There appears to be a race condition of some sort that was introduced at some point, investigating now.

[WardF]

#2964 is merged, looking for the race condition in the failed tests.