python-libcst upgrade and python-flake8

[jgart]

Hi Guixers,

What do suggest as a recommended fix for this error?

```
============================= 482 passed in 3.80s ==============================
phase `check' succeeded after 5.0 seconds
starting phase `sanity-check'
validating 'flake8' 
/gnu/store/zaw5z708sldm6v3qxjczcia7gl65dw5x-python-flake8-3.9.2/lib/python3.9/site-packages
...checking requirements: ERROR: flake8==3.9.2 
ContextualVersionConflict(pyflakes 2.4.0 
(/gnu/store/mxkp1zl64cd3i247shp7njkxad8v13x9-python-pyflakes-2.4.0/lib/python3.9/site-packages),
 Requirement.parse('pyflakes<2.4.0,>=2.3.0'), {'flake8'})
error: in phase 'sanity-check': uncaught exception:
%exception #<&invoke-error program: "python" arguments: 
("/gnu/store/35ix1m6m8a5s21j02ajhdyqxb2xkshfb-sanity-check.py" 
"/gnu/store/zaw5z708sldm6v3qxjczcia7gl65dw5x-python-flake8-3.9.2/lib/python3.9/site-packages")
 exit-status: 1 term-signal: #f stop-signal: #f> 
phase `sanity-check' failed after 0.2 seconds
command "python" "/gnu/store/35ix1m6m8a5s21j02ajhdyqxb2xkshfb-sanity-check.py" 
"/gnu/store/zaw5z708sldm6v3qxjczcia7gl65dw5x-python-flake8-3.9.2/lib/python3.9/site-packages"
 failed with status 1
builder for 
`/gnu/store/khh67agxwf3rvbrrph2m4x0ki7b0my2c-python-flake8-3.9.2.drv' failed 
with exit code 1
build of /gnu/store/khh67agxwf3rvbrrph2m4x0ki7b0my2c-python-flake8-3.9.2.drv 
failed
Could not find build log for 
'/gnu/store/khh67agxwf3rvbrrph2m4x0ki7b0my2c-python-flake8-3.9.2.drv'.
building 
/gnu/store/grfg324ljk5hpkwqq45pw99klxjib4bm-python-libcst-minimal-0.4.3.drv...
cannot build derivation 
`/gnu/store/5amv1366vcs79l3z0jfpd1c6s5w0315b-python-pylama-7.7.1.drv': 1 
dependencies couldn't be built
cannot build derivation 
`/gnu/store/k6nw3cj8ckd3ss9v7a73km47wz27mkfw-python-isort-5.10.1.drv': 1 
dependencies couldn't be built
cannot build derivation 
`/gnu/store/dd8qjvk6cd3xxfl6vspax6vbp3yyiix2-python-libcst-0.4.3.drv': 1 
dependencies couldn't be built
guix build: error: build of 
`/gnu/store/dd8qjvk6cd3xxfl6vspax6vbp3yyiix2-python-libcst-0.4.3.drv' failed
```

I was trying to upgrade python-libcst:

http://dpaste.com/AQDS5XW42 

Should I package a new version of flake8 that doesn't have a version conflict 
or patch out libcst?

all best,

jgart