Fix Max Residual Output for Incompressible Flow

[rois1995]

Proposed Changes

Just a small bug fix on the history output of the incompressible solver. The RMS-Velocity_Z value was overwritten by the RMS-Velocity_Z value. Already updated the tutorials and regression cases as it is just an output bug.

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
• I used the pre-commit hook to prevent dirty commits and used pre-commit run --all to format old commits.
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.