Adjust test to error message change in #53778

I considered changing the error message back, but I actually think
non-escaped filenames make more sense here, so I just adjusted
the test. We can do either though.

Author: Keno

test/loading.jl

@@ -1542,7 +1542,7 @@ end
         end
 
         file = joinpath(depot, "dev", "non-existent.jl")
-        @test_throws SystemError("opening file $(repr(file))") include(file)
+        @test_throws SystemError("opening file \"$file\"") include(file)
     end
 end