Add numba constraint

So we're compatible with astral-sh/uv#7881. Notes inline

pyproject.toml

@@ -27,8 +27,13 @@ dependencies = [
   "pandas>=2.1",
 ]
 
+# We don't encode minimum requirements here (though if we can write a script to
+# generate the text from `min_deps_check.py`, that's welcome...). We do add
+# `numba>=0.54` here because of https://github.com/astral-sh/uv/issues/7881;
+# note that it's not a direct dependency of xarray.
+
 [project.optional-dependencies]
-accel = ["scipy", "bottleneck", "numbagg", "flox", "opt_einsum"]
+accel = ["scipy", "bottleneck", "numbagg", "numba>=0.54", "flox", "opt_einsum"]
 complete = ["xarray[accel,etc,io,parallel,viz]"]
 dev = [
   "hypothesis",