Make write return Int instead of UInt in an obscure code-path. (JuliaLang#54197)

Author: LilithHafner

base/io.jl

@@ -804,7 +804,7 @@ unsafe_write(s::IO, p::Ptr, n::Integer) = unsafe_write(s, convert(Ptr{UInt8}, p)
 function write(s::IO, x::Ref{T}) where {T}
     x isa Ptr && error("write cannot copy from a Ptr")
     if isbitstype(T)
-        unsafe_write(s, x, Core.sizeof(T))
+        Int(unsafe_write(s, x, Core.sizeof(T)))
     else
         write(s, x[])
     end

test/filesystem.jl

@@ -46,3 +46,7 @@ end
   @test_broken isempty(undoc)
   @test undoc == [:File, :Filesystem, :cptree, :futime, :rename, :sendfile, :unlink]
 end
+
+@testet "write return type" begin
+    @test Base.return_types(write, (Base.Filesystem.File, UInt8)) == [Int]
+end