tests/basics: Skip exception_chain and self_type_check on unix minimal.

These two tests can't run on the unix minimal build because it doesn't have
the relevant build options enabled.  So skip them.

Signed-off-by: Damien George <damien@micropython.org>

tests/basics/exception_chain.py

@@ -1,6 +1,13 @@
 # Exception chaining is not supported, but check that basic
 # exception works as expected.
 
+import sys
+
+# The unix minimal build doesn't enable MICROPY_WARNINGS (required for this test).
+if getattr(sys.implementation, "_build", None) == "minimal":
+    print("SKIP")
+    raise SystemExit
+
 try:
     raise Exception from None
 except Exception:

tests/basics/self_type_check.py

@@ -1,5 +1,13 @@
 # make sure type of first arg (self) to a builtin method is checked
 
+import sys
+
+# Minimal builds usually don't enable MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG,
+# which is required for this test.
+if getattr(sys.implementation, "_build", None) == "minimal":
+    print("SKIP")
+    raise SystemExit
+
 list.append
 
 try: