[OpenMP] Fix child processes to use affinity_none (#91391)

When a child process is forked with OpenMP already initialized, the
child process resets its affinity mask and sets proc-bind-var to false
so that the entire original affinity mask is used. This patch corrects
an issue with the affinity initialization code setting affinity to
compact instead of none for this special case of forked children.

The test trying to catch this only testing explicit setting of
KMP_AFFINITY=none. Add test run for no KMP_AFFINITY setting.

Fixes: #91098