Pin proj to 9.3.0 in cuproj (#1307)

Currently `pyproj` is still pinned to `proj` 9.3.0 (for [example]( https://github.com/conda-forge/pyproj-feedstock/blob/1cd88219a34c40265a8f70384476ce6c90e1ac45/.ci_support/linux_64_numpy1.26python3.12.____cpython.yaml#L19-L20 )). However `proj` recently released `9.3.1` ( conda-forge/proj.4-feedstock#140 ), which `cuproj` is pulling in at the moment. Since `proj` [pins to the patch version in its `run_exports`]( https://github.com/conda-forge/proj.4-feedstock/blob/332baf3b6a739377f5e5cf65d9e9297d02a6ddf3/recipe/meta.yaml#L15-L18 ), building against `9.3.1` means `cuproj` would need exactly `9.3.1` at runtime. This makes it incompatible with everything else, which is still pinned to `proj` `9.3.0`. Embedded screenshot below to highlight this

So for now just manually pin `proj` to `9.3.0` to build `cuproj` with a consistent `proj` version to resolve conflicts

This issue should clear up once to `proj` `9.3.1` migration ( conda-forge/conda-forge-pinning-feedstock#5226 ) completes. Then we can bump this or drop it as we see fit then

Authors:
   - https://github.com/jakirkham

Approvers:
   - Bradley Dice (https://github.com/bdice)
   - Mark Harris (https://github.com/harrism)
   - Ray Douglass (https://github.com/raydouglass)

conda/recipes/cuproj/conda_build_config.yaml

@@ -15,3 +15,7 @@ sysroot_version:
 
 cmake_version:
   - ">=3.26.4"
+
+# Workaround until proj 9.3.1 migration completes
+proj:
+  - "9.3.0"