Do not apply double slash to Blueprint and static dirs

[ahopkins]

Fixes #2514

[codecov]

Codecov Report

Base: 87.450% // Head: 87.528% // Increases project coverage by +0.078% 🎉

Coverage data is based on head (d694d1f) compared to base (e499940).
Patch coverage: 100.000% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2515       +/-   ##
=============================================
+ Coverage   87.450%   87.528%   +0.078%     
=============================================
  Files           69        69               
  Lines         5602      5613       +11     
  Branches       974       976        +2     
=============================================
+ Hits          4899      4913       +14     
+ Misses         509       507        -2     
+ Partials       194       193        -1     

Impacted Files	Coverage Δ
sanic/blueprints.py	91.176% <100.000%> (+0.407%)	⬆️
sanic/mixins/routes.py	93.750% <100.000%> (+0.049%)	⬆️
sanic/server/protocols/http_protocol.py	83.823% <0.000%> (+2.205%)	⬆️

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[Tronic]

Works for me. Thanks for the quick fix!

Note: url_prefix should end with a slash for blueprints intended to run as a folder (or at site root), otherwise "" route still becomes a file (which OTOH can make sense for blueprints that only have that one endpoint).