Bump main to 7.0.0~pre1

[chapulina]

Part of gazebo-tooling/release-tools#459

[codecov]

Codecov Report

Merging #301 (d5431c5) into main (53360bb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #301   +/-   ##
=======================================
  Coverage   65.47%   65.47%           
=======================================
  Files          32       32           
  Lines        4686     4686           
=======================================
  Hits         3068     3068           
  Misses       1618     1618           

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