Fix: use adapter.get_columns_in_relation (#5232)

Author: jtcohen6

.changes/unreleased/Fixes-20220511-123238.yaml

@@ -0,0 +1,7 @@
+kind: Fixes
+body: Fix column comparison in snapshot_check_all_get_existing_columns to use adapter.get_columns_in_relation
+time: 2022-05-11T12:32:38.313321+02:00
+custom:
+  Author: jtcohen6
+  Issue: "5222"
+  PR: "5232"

core/dbt/include/global_project/macros/materializations/snapshots/strategies.sql

@@ -126,7 +126,7 @@
         {% do exceptions.raise_compiler_error("Invalid value for 'check_cols': " ~ check_cols_config) %}
     {% endif %}
 
-    {%- set existing_cols = get_columns_in_relation(target_relation) | map(attribute = 'name') | list -%}
+    {%- set existing_cols = adapter.get_columns_in_relation(target_relation) | map(attribute = 'name') | list -%}
     {%- set ns = namespace() -%} {#-- handle for-loop scoping with a namespace --#}
     {%- set ns.column_added = false -%}