allow to override the LAMMPS dll location on windows

this is to work around the situation that windows
has no equivalent to LD_LIBRARY_PATH (short of augmenting %PATH%,
which is tricky for CMake before 3.20)

python/lammps/core.py

@@ -89,6 +89,9 @@ class lammps(object):
     modpath = dirname(abspath(getsourcefile(lambda:0)))
     # for windows installers the shared library is in a different folder
     winpath = abspath(os.path.join(modpath,'..','..','bin'))
+    # allow override for running tests on Windows
+    if (os.environ.get("LAMMPSDLLPATH")):
+      winpath = os.environ.get("LAMMPSDLLPATH")
     self.lib = None
     self.lmp = None