Respect sys.flags.safe_path

[siddharthab]

In the following line, the script directory path is added even if Python was run with sys.flags.safe_path (most often by setting the env var PYTHONSAFEPATH=1).

ipykernel/hatch_build.py

Line 15 in b11d42c

sys.path.insert(0, str(here))

Not having the ability to set safe path causes problems when there are sibling Python files with names that clash with installed Python modules.

Thanks to @DonJayamanne for helping find the root cause in microsoft/vscode-jupyter#16235.