Fix issue #8578. Setting envvar in ""'s ensures the PYTHONPATH is set to

include the lib/ directory.

Before - PYTHONPATH is empty.. ansible fails to run

    $ source hacking/env-setup.fish
    Appending PYTHONPATH

    Setting up Ansible to run out of checkout...

    PATH=/Volumes/opt/src/ansible/bin /usr/local/share/python3 /usr/local/bin
    /usr/bin /bin /usr/sbin /sbin /usr/local/bin /opt/X11/bin /usr/bin /sbin
    /usr/local/bin /Users/ms/bin/
    PYTHONPATH=
    ANSIBLE_LIBRARY=/Volumes/opt/src/ansible/library
    ...

    Traceback (most recent call last):
      File "/Volumes/opt/src/ansible/bin/ansible", line 25, in <module>
          from ansible.runner import Runner
          ImportError: No module named ansible.runner

After change - it's set.. ansible runs.

    source hacking/env-setup.fish
    Appending PYTHONPATH

    Setting up Ansible to run out of checkout...

    PATH=/Volumes/opt/src/ansible/bin /usr/local/share/python3 /usr/local/bin
    /usr/bin /bin /usr/sbin /sbin /usr/local/bin /opt/X11/bin /usr/bin /sbin
    /usr/local/bin /Users/ms/bin/
    PYTHONPATH=/Volumes/opt/src/ansible/lib:
    ANSIBLE_LIBRARY=/Volumes/opt/src/ansible/library
    ....

    $ ansible
    Usage: ansible <host-pattern> [options]

hacking/env-setup.fish

@@ -16,7 +16,7 @@ else
         case "$PREFIX_PYTHONPATH*"
         case "*"
             echo "Appending PYTHONPATH"
-            set -gx PYTHONPATH $PREFIX_PYTHONPATH:$PYTHONPATH
+            set -gx PYTHONPATH "$PREFIX_PYTHONPATH:$PYTHONPATH"
     end
 end