Upgrade Elixir to 1.18 and OTP to 27

[stuartc]

Description

This PR upgrades the Elixir version to 1.18.3 and OTP to 27.3.3

Closes #3153

Validation steps

1. clone the repo
2. run /bin/bootstrap
3. run mix test

AI Usage

Please disclose how you've used AI in this work (it's cool, we just want to know!):

• [ ] Code generation (copilot but not intellisense)
• [ ] Learning or fact checking
• [ ] Strategy / design
• [ ] Optimisation / refactoring
• [ ] Translation / spellchecking / doc gen
• [ ] Other
• [x] I have not used AI

You can read more details in our Responsible AI Policy

Pre-submission checklist

• [x] I have performed a self-review of my code.
• [x] I have implemented and tested all related authorization policies. (e.g., :owner, :admin, :editor, :viewer)
• [ ] I have updated the changelog.
• [x] I have ticked a box in "AI usage" in this PR

[rorymckinley]

@stuartc Happy for me to push this over the finish line?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.45%. Comparing base (a6ee153) to head (db96113).

Files with missing lines	Patch %	Lines
lib/lightning_web/live/dev/components_live.ex	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2748      +/-   ##
==========================================
- Coverage   91.51%   91.45%   -0.07%     
==========================================
  Files         359      359              
  Lines       13632    13672      +40     
==========================================
+ Hits        12476    12504      +28     
- Misses       1156     1168      +12     

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[rorymckinley]

PS: I can't see what Codecov is complaining about :)

[stuartc]

PS: I can't see what Codecov is complaining about :)

Hmm looks likes indirect changes, they look innocuous to me.

[jyeshe]

@rorymckinley , @stuartc has identified a possible cause in his environment and asked us to move on with this. I could compile on Mac without any intervention.

We've agreed upon upgrading Elixir to 1.18, for the extended type checking. Would you like to give it a try with the 1.18 as well?