Python: Teach py/unreachable-statement about contextlib.suppress.

python/ql/test/3/query-tests/Statements/unreachable_suppressed/UnreachableCode.qlref

@@ -0,0 +1 @@
+Statements/UnreachableCode.ql

python/ql/test/3/query-tests/Statements/unreachable_suppressed/test.py

@@ -0,0 +1,31 @@
+from contextlib import suppress
+
+def raises_exception():
+    raise Exception("This will be suppressed")
+
+def foo():
+    test = False
+    with suppress(Exception):
+        raises_exception()
+        test = True
+    if test:
+        return
+    print("An exception was raised") # FP: not reached
+
+foo()
+
+def bar(x):
+    test = False
+    try:
+        if x:
+            raise Exception("Bar")
+        test = True
+    except Exception:
+        pass
+    if test:
+        print("Test was set")
+        return
+    print("Test was not set")
+
+bar(True)
+bar(False)