Unclear error message when no-data cannot be updated in geoid file

In cache_dem_by: symlink mode, if the geoid file is read-only, the following (obscure) error will be logged:

2025-12-19 15:34:33,777 - s1tiling.utils  - DEBUG    - Fetch No-data value from '/my/work/space/tmp/geoid/egm08_25.gtx'
2025-12-19 15:34:33,843 - s1tiling.workspace - DEBUG    - '/my/work/space/tmp/geoid/egm08_25.gtx' nodata is -88.8888
2025-12-19 15:34:33,843 - s1tiling.utils  - DEBUG    - Set No-data value to -32768 in '/my/work/space/tmp/geoid/egm08_25.gtx'
2025-12-19 15:34:33,843 - s1tiling.cli    - CRITICAL - /my/work/space/tmp/geoid/egm08_25.gtx: Permission denied

Unless logs are in debug mode, it's quite difficult to understand that an attempt at fixing a suspicious no-data value ([a61ac31c]) has failed because the Geoid file couldn't be written.