Issue #16840: Skip bignum tests on minor releases where they are not supported.

Lib/test/test_tcl.py

@@ -130,7 +130,9 @@ class TclTest(unittest.TestCase):
         integers = (0, 1, -1, 2**31-1, -2**31)
         if tcl_version >= (8, 4):  # wideInt was added in Tcl 8.4
             integers += (2**31, -2**31-1, 2**63-1, -2**63)
-        if tcl_version >= (8, 5):  # bignum was added in Tcl 8.5
+        # bignum was added in Tcl 8.5, but its support is able only since 8.5.8
+        if (get_tk_patchlevel() >= (8, 6, 0, 'final') or
+            (8, 5, 8) <= get_tk_patchlevel() < (8, 6)):
             integers += (2**63, -2**63-1, 2**1000, -2**1000)
         return integers