filter out duplicate modules in auto-install search, fixes #42133 (#42134)

(cherry picked from commit f2d03be)

Author: IanButterworth

stdlib/REPL/src/REPL.jl

@@ -196,7 +196,7 @@ function modules_to_be_loaded(ast::Expr, mods::Vector{Symbol} = Symbol[])
         arg isa Expr && modules_to_be_loaded(arg, mods)
     end
     filter!(mod -> !in(String(mod), ["Base", "Main", "Core"]), mods) # Exclude special non-package modules
-    return mods
+    return unique(mods)
 end
 
 """

stdlib/REPL/test/repl.jl

@@ -1332,6 +1332,8 @@ end
         @test mods == [:Foo, :Bar]
         mods = REPL.modules_to_be_loaded(Base.parse_input_line("import Foo, Bar"))
         @test mods == [:Foo, :Bar]
+        mods = REPL.modules_to_be_loaded(Base.parse_input_line("using Foo.bar, Foo.baz"))
+        @test mods == [:Foo]
 
         mods = REPL.modules_to_be_loaded(Base.parse_input_line("if false using Foo end"))
         @test mods == [:Foo]