tests/basics/string_join: Add more tests for string concatenation.

tests/basics/string_join.py

@@ -25,3 +25,13 @@ except TypeError:
 
 # joined by the compiler
 print("a" "b")
+print("a" '''b''')
+print("a" # inline comment
+    "b")
+print("a" \
+    "b")
+
+# the following should not be joined by the compiler
+x = 'a'
+'b'
+print(x)