Remove 'dbt-core<1.8.9' pin

[tatiana]

We were facing issues with conflicting dbt core and dbt-databricks when using the latest release of dbt-core:

File "<frozen importlib._bootstrap>", line 1204, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1176, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1147, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 690, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line [940](https://github.com/astronomer/astronomer-cosmos/actions/runs/12018236731/job/33502297498?pr=1340#step:7:941), in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/home/runner/.local/share/hatch/env/virtual/astronomer-cosmos/Za_bFbg4/tests.py3.11-2.6/lib/python3.11/site-packages/dbt/adapters/databricks/__init__.py", line 1, in <module>
    from dbt.adapters.databricks.connections import DatabricksConnectionManager  # noqa
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/.local/share/hatch/env/virtual/astronomer-cosmos/Za_bFbg4/tests.py3.11-2.6/lib/python3.11/site-packages/dbt/adapters/databricks/connections.py", line 27, in <module>
    from dbt.adapters.base import Credentials
ImportError: cannot import name 'Credentials' from 'dbt.adapters.base' (/home/runner/.local/share/hatch/env/virtual/astronomer-cosmos/Za_bFbg4/tests.py3.11-2.6/lib/python3.11/site-packages/dbt/adapters/base/__init__.py)

This PR solves this.

Closes: #1343

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.02%. Comparing base (c606bcb) to head (7c18bf4).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1371   +/-   ##
=======================================
  Coverage   96.02%   96.02%           
=======================================
  Files          67       67           
  Lines        4025     4025           
=======================================
  Hits         3865     3865           
  Misses        160      160           

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