[HOTFIX] use srtm1 data to see even more contour lines + upgrade GDAL from 3.4 to 3.6

[treee111]

This PR…

• fixes comments of #145

Considerations and implementations

shipping as hotfix so that creation of Anaconda environment needs to be only done once for v4.0.x and not several times because one dependency was bumped.

How to test

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Pull Request Checklist

• [x] Reviewed the Contributing Guidelines
  • Especially the Pull-Requests section
• [x] Commits (and commit-messages) are understandable
• [ ] Tested with macOS / Linux
• [ ] Tested with Windows