Update Heightmaps tutorial screenshot

[iche033]

🦟 Bug fix

Summary

The current screenshot seems to be from ogre 1.x. When running the tutorial instructions ./heightmaps --dem, it launched the demo with ogre2 so I updated screenshots to match.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #716 (496e4e9) into gz-rendering7 (d3d691e) will not change coverage.
The diff coverage is n/a.

❗ Current head 496e4e9 differs from pull request most recent head 6caefca. Consider uploading reports for the commit 6caefca to get more accurate results

@@              Coverage Diff               @@
##           gz-rendering7     #716   +/-   ##
==============================================
  Coverage          74.14%   74.14%           
==============================================
  Files                164      164           
  Lines              14351    14351           
==============================================
  Hits               10641    10641           
  Misses              3710     3710           

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