Test for no ambiguities

Julia itself tests for no ambiguities in its stdlibs. This means StyledStrings
tests may pass, only to fail in Julia when trying to bump this stdlib.
Add tests for no ambiguities to this package to preempt this early.

Author: jakobnissen

test/runtests.jl

@@ -9,6 +9,8 @@ using .StyledMarkup: MalformedStylingMacro
 
 @test isempty(Test.detect_closure_boxes(StyledStrings))
 
+@test isempty(Test.detect_ambiguities(StyledStrings))
+
 const NON_STDLIB_TESTS = Main == @__MODULE__
 if NON_STDLIB_TESTS
     include("styfuzz.jl") # For use in the "Styled Markup" testset