Update Data-Sources.md with new links to GTFS.org from MobilityData [ci skip]

[BredeD]

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Summary

Update the website with URL to MobilityData GTFS.org webpabe.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.74%. Comparing base (d2f4b2d) to head (e6622b8).
Report is 12 commits behind head on dev-2.x.

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #6034      +/-   ##
=============================================
- Coverage      69.74%   69.74%   -0.01%     
+ Complexity     17316    17315       -1     
=============================================
  Files           1960     1960              
  Lines          74267    74267              
  Branches        7603     7603              
=============================================
- Hits           51796    51794       -2     
- Misses         19829    19831       +2     
  Partials        2642     2642              

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