Add return value to AdapterContainer.__init__ and AdapterMeta.__new__

[gshank]

resolves #8387

Problem

Mypy warnings because of lack of return value for functions.

Solution

Adds return values.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.05% ⚠️

Comparison is base (770f804) 86.35% compared to head (f615f6a) 86.31%.
Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8523      +/-   ##
==========================================
- Coverage   86.35%   86.31%   -0.05%     
==========================================
  Files         174      174              
  Lines       25561    25579      +18     
==========================================
+ Hits        22074    22079       +5     
- Misses       3487     3500      +13     

Flag	Coverage Δ
integration	83.09% <100.00%> (-0.11%)	⬇️
unit	65.14% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
core/dbt/adapters/base/meta.py	98.11% <100.00%> (ø)
core/dbt/adapters/factory.py	91.89% <100.00%> (ø)

... and 16 files with indirect coverage changes

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