Missing f prefix on f-strings fix

[code-review-doctor]

Fixes #7480

[lgtm-com]

This pull request introduces 1 alert when merging 8198914 into 969e36a - view on LGTM.com

new alerts:

• 1 for Module is imported with 'import' and 'import from'

[codecov]

Codecov Report

Merging #7481 (8198914) into master (fe0e50e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7481   +/-   ##
=======================================
  Coverage   89.27%   89.27%           
=======================================
  Files         138      138           
  Lines       16788    16788           
  Branches     2454     2454           
=======================================
  Hits        14988    14988           
  Misses       1568     1568           
  Partials      232      232           

Flag	Coverage Δ
unittests	89.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
celery/backends/dynamodb.py	97.75% <ø> (ø)
celery/backends/asynchronous.py	67.09% <0.00%> (ø)

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