Update datashader pin (#658)

Updates the `datashader` to match rapidsai/cuxfilter#479

I confirmed this works locally.

Authors:
   - Ray Douglass (https://github.com/raydouglass)

Approvers:
   - Jake Awe (https://github.com/AyodeAwe)
   - AJ Schmidt (https://github.com/ajschmidt8)

conda/recipes/versions.yaml

@@ -53,7 +53,7 @@ cython_version:
 dask_version:
   - '==2023.3.2'
 datashader_version:
-  - '>=0.14,<=0.14.4'
+  - '>=0.15'
 distributed_version:
   - '==2023.3.2.1'
 dlpack_version: