Flexibilize MarkupSafe pinned version

The current `MarkupSafe` pinned version has been added in dbt-labs#4746 as a
temporary fix for dbt-labs#4745.

However, the current restrictive approach isn't compatible with other
libraries that could require an even older version of `MarkupSafe`, like
Airflow `2.2.2` [0], which requires `markupsafe>=1.1.1, <2.0`.

To avoid that issue, we can allow a greater range of supported
`MarkupSafe` versions. Considering the direct dependency `dbt-core` has
is `Jinja2==2.11.3`, we can use its pinning as the lower bound, which is
`MarkupSafe>=0.23` [1].

This fix should be also backported this to `1.0.latest` for inclusion in
the next v1.0 patch.

[0] https://github.com/adamantike/airflow/blob/2.2.2/setup.cfg#L125
[1] https://github.com/pallets/jinja/blob/2.11.3/setup.py#L53

core/setup.py

@@ -52,7 +52,7 @@
     ],
     install_requires=[
         "Jinja2==2.11.3",
-        "MarkupSafe==2.0.1",
+        "MarkupSafe>=0.23,<2.1",
         "agate>=1.6,<1.6.4",
         "click>=7.0,<9",
         "colorama>=0.3.9,<0.4.5",