Remove unnecessary LIST_TO_TUPLE conversions

[brandtbucher]

This probably doesn't need an issue or NEWS, it's just a little inefficiency @markshannon noticed earlier today. Basically, it doesn't matter if we're actually iterating over a tuple, so if we already have a list with the correct items, use that instead.

[markshannon]

Looks sound.

I thought this might break the following code:

def f():                                                                                                                                       
    for i in (*(l:= [1,2,3]),):
        x = l.pop()
        print(i)

It doesn't seem to as it builds a fresh list before converting it to a tuple, but could you add this code as a test case.
Otherwise things might break if we remove the extra LIST_EXTEND

[bedevere-app]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[brandtbucher]

I have made the requested changes; please review again

[bedevere-app]

Thanks for making the requested changes!

@markshannon: please review the changes made to this pull request.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 RHEL8 LTO + PGO 3.x has failed when building commit 004f9fd.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/78/builds/8163) and take a look at the build logs.
4. Check if the failure is related to this commit (004f9fd) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/78/builds/8163

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/threading.py", line 1054, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/threading.py", line 996, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/test/test_interpreters/test_stress.py", line 30, in task
    interp = interpreters.create()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/test/support/interpreters/__init__.py", line 76, in create
    id = _interpreters.create(reqrefs=True)
interpreters.InterpreterError: interpreter creation failed
k


Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/threading.py", line 1054, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/threading.py", line 996, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/test/test_interpreters/test_stress.py", line 47, in run
    interp = interpreters.create()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-aarch64.lto-pgo/build/Lib/test/support/interpreters/__init__.py", line 76, in create
    id = _interpreters.create(reqrefs=True)
interpreters.InterpreterError: interpreter creation failed
k