Resolve warning that will affect Python 3.10 compatibility

I noticed this message during an otherwise successful build of
our arduino-CAN fork:

/home/runner/work/arduino-CAN/arduino-CAN/ci/build_platform.py:183: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.10 it will stop working

This should resolve the problem.

build_platform.py

@@ -180,7 +180,7 @@ for arg in sys.argv[1:]:
     platform = ALL_PLATFORMS.get(arg, None)
     if isinstance(platform, str):
         platforms.append(arg)
-    elif isinstance(platform, collections.Iterable):
+    elif isinstance(platform, collections.abc.Iterable):
         for p in platform:
             platforms.append(p)
     else: