feat(PECOBLR-2328): bump databricks-sql-connector upper bound to <4.1.6 (#1363)

## Summary

- Bumps `databricks-sql-connector` upper bound from `<4.1.4` to
`<4.1.6`, allowing users to install connector `4.1.5`
- Connector `4.1.5` introduced
[`_respect_server_retry_after_header`](databricks/databricks-sql-python#756),
which users can now opt into via `connection_parameters` in
`profiles.yml`

## Context

Customers using `use_materialization_v2: true` experience duplicate rows
when the server returns HTTP 503 after already committing an INSERT. The
connector blindly retries, causing data to be written twice. With
`_respect_server_retry_after_header: true`, retries only occur when the
server explicitly sends a `Retry-After` header, preventing duplicate
writes from infrastructure-level 503s.

## Test plan

- [x] All 744 unit tests pass (`hatch run unit`)
- [x] E2E verification with a dummy dbt project against UC SQL endpoint:
- `dbt debug` + `dbt run` succeed with default profile (connector
default `False` applied)
- `dbt debug` + `dbt run` succeed with
`_respect_server_retry_after_header: true` explicitly set

---------

Co-authored-by: Shubham Dhal <shubham.dhal@databricks.com>

Author: tejassp-db

CHANGELOG.md

@@ -13,6 +13,7 @@
 
 ### Under the Hood
 
+- Bump `databricks-sql-connector` upper bound to `<4.1.6`, enabling users to opt into `_respect_server_retry_after_header` (available in connector 4.1.5) for server-directed retry behavior via `connection_parameters` ([#1363](https://github.com/databricks/dbt-databricks/pull/1363))
 - Bump upper bound of dbt-core to `<1.11.9` to include dbt-core 1.11.8
 
 ## dbt-databricks 1.11.6 (Mar 10, 2026)

pyproject.toml

@@ -24,7 +24,7 @@ classifiers = [
 dependencies = [
     "click>=8.2.0, <9.0.0",
     "databricks-sdk>=0.68.0, <0.78.0",
-    "databricks-sql-connector[pyarrow]>=4.1.1, <4.1.4",
+    "databricks-sql-connector[pyarrow]>=4.1.1, <4.1.6",
     "dbt-adapters>=1.22.0, <1.23.0",
     "dbt-common>=1.37.0, <1.38.0",
     "dbt-core>=1.11.2, <1.11.9",