install rasterio explicitly as a workaround to fix the missing rasterio

[TejasMorbagal]

[Description of PR]

install rasterio explicitly as a workaround to fix the missing rasterio issue in xcube docker image

Checklist:

~ [ ] Add unit tests and/or doctests in docstrings~ ~ [ ] Add docstrings and API docs for any new/modified user-facing classes and functions~ ~ [ ] New/modified features documented in `docs/source/`~

• [ ] Changes documented in CHANGES.md
• [ ] GitHub CI passes
• [ ] AppVeyor CI passes
• [ ] Test coverage remains or increases (target 100%)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (6dd9689) 93.33% compared to head (4f0941f) 93.33%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #911 +/- ## ======================================= Coverage 93.33% 93.33% ======================================= Files 447 447 Lines 34924 34924 ======================================= Hits 32596 32596 Misses 2328 2328 ```

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