Change ownership of src/config.inc file

[NlightNFotis]

Change ownership of src/config.inc file to @diffblue/diffblue-opensource

This is a minor change to allow for faster releases, by requiring less people
to sign off a release PR (it is now okay if it's signed off by a member of the
team maintaining CBMC in diffblue - the people that have been handling releases
in any case).

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #6373 (54a50e9) into develop (fcca0e5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #6373   +/-   ##
========================================
  Coverage    75.91%   75.91%           
========================================
  Files         1517     1517           
  Lines       164024   164024           
========================================
  Hits        124515   124515           
  Misses       39509    39509           

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