todo test for GH 2027 (Code blessed where it shouldn't)

[1-1sam]

This PR adds a todo test for #2027 which tests that perl does not re-use the same subroutine reference when passing distinct subs to a function. This test still appears to fail.

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• This set of changes does not require a perldelta entry.

[jkeenan]

When I build a perl from the branch in this p.r., then run t/run/todo.t,I get output like this:

not ok 2 - The same subroutine reference is not re-used when blessed; GH 2027 # TODO GH 2027
# Failed test 2 - The same subroutine reference is not re-used when blessed; GH 2027 at t/run/todo.t line 143
# it should not be "main=CODE(0x6117471c0df0)"
# but it is.

I don't see where the last two lines (starting with # it should not be) are coming from. Can you clarify? Thanks.

[1-1sam]

Those two lines are messages from the isnt() test from test.pl.