Refactor deprecated DBConnection function call

[robinwiel]

The calls to getConnectionRef have been deprecated since MediaWiki 1.39. getConnectionRef() already redirects to getConnection(), but now we call this function directly to remove deprecation notices.

[robinwiel]

@JeroenDeDauw could you check? was CI broken already for 1.43?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.12%. Comparing base (1bb9e88) to head (0f00f39).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #114   +/-   ##
=========================================
  Coverage     76.12%   76.12%           
  Complexity      719      719           
=========================================
  Files            36       36           
  Lines          2325     2325           
=========================================
  Hits           1770     1770           
  Misses          555      555           

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[alistair3149]

The CI is broken prior and unrelated to this PR.
Changes LGTM, thanks for submitting the PR! 🎉