Change sync disposal warning message adjective from efficient -> inefficient

[alistairjevans]

Noticed this typo while updating docs.

[codecov]

Codecov Report

Merging #1323 (c69da54) into develop (78c47f5) will increase coverage by 0.40%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #1323      +/-   ##
===========================================
+ Coverage    76.84%   77.25%   +0.40%     
===========================================
  Files          188      190       +2     
  Lines         5191     5513     +322     
  Branches      1064     1105      +41     
===========================================
+ Hits          3989     4259     +270     
- Misses         703      736      +33     
- Partials       499      518      +19     

Impacted Files	Coverage Δ
src/Autofac/Util/SequenceGenerator.cs	71.42% <0.00%> (-28.58%)	⬇️
src/Autofac/ResolveRequest.cs	100.00% <0.00%> (ø)
...ore/Resolving/BaseGenericResolveDelegateInvoker.cs	100.00% <0.00%> (ø)
...degen/Autofac.CodeGen/DelegateRegisterGenerator.cs	97.63% <0.00%> (ø)
src/Autofac/ResolutionExtensions.cs	51.76% <0.00%> (+0.62%)	⬆️

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[tillig]

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