Run test for autogenerated config in subprocess (#47)

Only a single version of a dotnet-core runtime can be loaded at a given
time. This off-loads one of our tests to a subprocess (the same pattern
would work if we did this for the other test). Could be cleaner, but
this will do for now.

tests/test_common.py

@@ -57,6 +57,17 @@ def test_coreclr(example_netcore):
 
 
 def test_coreclr_autogenerated_runtimeconfig(example_netstandard):
+    from multiprocessing import get_context
+
+    p = get_context("spawn").Process(
+        target=_do_test_coreclr_autogenerated_runtimeconfig, args=(example_netstandard,)
+    )
+    p.start()
+    p.join()
+    p.close()
+
+
+def _do_test_coreclr_autogenerated_runtimeconfig(example_netstandard):
     from clr_loader import get_coreclr
 
     coreclr = get_coreclr()