⬆️ Upgrade to Elixir 1.16

[randycoulman]

Describe the purpose of your pull request

Elixir 1.11 is no longer supported, so remove from the CI matrix.

Update Credo to get some 1.16 fixes, which required disabling credo in a few places that now trigger false-positive rule violations. The functions in question are inlined in the config-v6 branch, so this temporary override will go away soon.

Related issues (only if applicable)

Provide links to issues relating to this pull request

Requirement checklist (only if applicable)

• I have covered the applied changes with automated tests.
• I have executed the full automated test set against my changes.
• I have validated my changes against all supported platform versions.
• I have read and accepted the contribution agreement.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (588a1d7) 94.77% compared to head (4e65f26) 94.28%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
lib/config_cat/config/setting_type.ex	0.00%	4 Missing ⚠️
lib/config_cat/cache_policy/null.ex	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #134      +/-   ##
==========================================
- Coverage   94.77%   94.28%   -0.50%     
==========================================
  Files          32       33       +1     
  Lines         766      770       +4     
==========================================
  Hits          726      726              
- Misses         40       44       +4     

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