install cf_units without wheels

Author: Romain

.github/workflows/ci.yml

@@ -51,6 +51,7 @@ jobs:
     - name: Install dependencies
       run: |
         uv sync --resolution ${{matrix.resolution}} --no-group docs
+        export UDUNITS2_XML_PATH=/usr/share/xml/udunits/udunits2.xml
         uv pip install cf_units==3.3.0
     - if: matrix.pint == 'with'
       name: Install pint and pint-xarray