refactor: drop support for Ibis 3.x

BREAKING CHANGE: The minimum supported version of Ibis is 4.0.
Deprecated methods `sort_by` and `groupby` have been removed in Ibis
6.x, so it is not possible to support 3.x through 6.x.

.github/workflows/ci.yml

@@ -98,9 +98,6 @@ jobs:
          - os: windows-latest
            python-version: "3.11"
            ibis-version: "5.1"
-         - os: ubuntu-latest
-           python-version: "3.10"
-           ibis-version: "3.2"
 
 
     steps:
@@ -136,10 +133,6 @@ jobs:
         ibis-version:
           - "4.1"
           - "5.1"
-        include:
-          - os: ubuntu-latest
-            python-version: "3.10"
-            ibis-version: "3.2"
 
     steps:
       - uses: actions/checkout@v3

ibis_substrait/compiler/core.py

@@ -110,9 +110,9 @@ def extension_lookup(
         if function_extension is None:
             sigkey = tuple(
                 [
-                    IBIS_SUBSTRAIT_TYPE_MAPPING[arg.op().output_dtype.name]  # type: ignore
+                    IBIS_SUBSTRAIT_TYPE_MAPPING[arg.output_dtype.name]  # type: ignore
                     for arg in op.args
-                    if arg is not None and isinstance(arg, (ir.Expr, ops.Node))
+                    if arg is not None and isinstance(arg, ops.Node)
                 ]
             )
             function_extension = _extension_mapping[op_name].get(sigkey)