bump version to 1.12.0

[emmyoop]

Description

Prep for 1.12.0 release to include

• Deprecate Python 3.8 (#212)
• Accelerate block tag iteration (#205)

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.48%. Comparing base (65d7ba5) to head (0f9d642).

Files with missing lines	Patch %	Lines
dbt_common/__about__.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #217   +/-   ##
=======================================
  Coverage   68.48%   68.48%           
=======================================
  Files          52       52           
  Lines        3389     3389           
=======================================
  Hits         2321     2321           
  Misses       1068     1068           

Flag	Coverage Δ
unit	68.48% <0.00%> (ø)

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