ctest: macOS `MallocGuardEdges` env var seems to interfere with OS detection

Consider this VTK build submission:

https://open.cdash.org/viewTest.php?onlynotrun&buildid=10040042

Notice the "OS name".

I enable the environment variable MallocGuardEdges to check for memory overruns when tests are run. (see man malloc on macOS). This causes a log message, for example:

% MallocGuardEdges=1 sw_vers
sw_vers(33753,0x202738f40) malloc: adding guard pages for large allocator blocks
ProductName:		macOS
ProductVersion:		14.7
BuildVersion:		23H124

versus without it:

% sw_vers
ProductName:		macOS
ProductVersion:		14.7
BuildVersion:		23H124

I believe this is why those 3 fields are scrambled. You should be able to look for ProductName then take the text after it.