sys.version_info reachability-check fails when patchlevel is specified in the version-condition

Bug Report

Apparent regression: mypy reachability check involving sys.version_info seems to fail when patchlevel is specified in the version condition.

To Reproduce

Run mypy CLI over the following code:

import sys

if sys.version_info < (3, 8, 0):
    import importlib_metadata as metadata
else:
    from importlib import metadata

my_metadata = metadata.metadata("mypy")  # just using mypy as an example here; could be any package's name

e.g.

mypy test.py

(tested under python 3.7)

Expected Behavior
Code should pass, with output like:

Success: no issues found in 1 source file

Actual Behavior

mypy reports issues, which appear to stem from a failure to flag some of the code as unreachable:

test.py:7: error: Module "importlib" has no attribute "metadata"
test.py:7: error: Name "metadata" already defined (by an import)
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.930
• Python version used: 3.7.6
• Operating system and version: MacOS Catalina 10.15.7

NOTES:

• The example works fine under mypy 0.910; fails under 0.920 and 0.930.
• The example works fine if the condition is changed to omit the python patchlevel, i.e. replace

if sys.version_info < (3, 8, 0):

with

if sys.version_info < (3, 8):

Run the supplied test.py example through the mypy CLI, comparing the three-component version condition with the two-component form and the reported behavior in mypy 0.910, 0.920, and 0.930. Trace the version-condition reachability check and verify that the unreachable import branch no longer produces errors, while the expected success output is preserved.