fix: show warning when hot is enabled with the HMR plugin in config

[snitin315]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

WIP on tests.

Motivation / Use-Case

show users a warning when hot is enabled with the HMR plugin in the configuration

Breaking Changes

None

Additional Info

No

[alexander-akait]

Let's add test, looks fine

[codecov]

Codecov Report

Merging #3744 (03a9189) into master (8f20c3e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3744   +/-   ##
=======================================
  Coverage   92.89%   92.90%           
=======================================
  Files          14       14           
  Lines        1323     1324    +1     
  Branches      466      465    -1     
=======================================
+ Hits         1229     1230    +1     
  Misses         87       87           
  Partials        7        7           

Impacted Files	Coverage Δ
lib/Server.js	93.86% <100.00%> (+<0.01%)	⬆️

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