fix a few tiny JET linter issues (JuliaLang#58869)

Author: KristofferC

base/loading.jl

@@ -184,8 +184,8 @@ end
 const slug_chars = String(['A':'Z'; 'a':'z'; '0':'9'])
 
 function slug(x::UInt32, p::Int)
-    y::UInt32 = x
     sprint(sizehint=p) do io
+        y = x
         n = length(slug_chars)
         for i = 1:p
             y, d = divrem(y, n)
@@ -1061,6 +1061,7 @@ function explicit_manifest_uuid_path(project_file::String, pkg::PkgId)::Union{No
     for (name, entries) in d
         entries = entries::Vector{Any}
         for entry in entries
+            entry = entry::Dict{String, Any}
             uuid = get(entry, "uuid", nothing)::Union{Nothing, String}
             extensions = get(entry, "extensions", nothing)::Union{Nothing, Dict{String, Any}}
             if extensions !== nothing && haskey(extensions, pkg.name) && uuid !== nothing && uuid5(UUID(uuid), pkg.name) == pkg.uuid

base/toml_parser.jl

@@ -258,10 +258,10 @@ end
 mutable struct ParserError <: Exception
     type::ErrorType
 
-    # Arbitrary data to store at the
+    # Data to store at the
     # call site to be used when formatting
     # the error
-    data
+    data::Union{Char, Nothing}
 
     # These are filled in before returning from parse function
     str       ::Union{String,   Nothing}
@@ -276,15 +276,15 @@ ParserError(type) = ParserError(type, nothing)
 # Defining these below can be useful when debugging code that erroneously returns a
 # ParserError because you get a stacktrace to where the ParserError was created
 #ParserError(type) = error(type)
-#ParserError(type, data) = error(type,data)
+#ParserError(type, data) = error(type, data)
 
 # Many functions return either a T or a ParserError
 const Err{T} = Union{T, ParserError}
 
 function format_error_message_for_err_type(error::ParserError)
     msg = err_message[error.type]
     if error.type == ErrInvalidBareKeyCharacter
-        c_escaped = escape_string(string(error.data)::String)
+        c_escaped = escape_string(string(error.data::Char))
         msg *= ": '$c_escaped'"
     end
     return msg