Add one more test example for swap instruction

[nvasilevski]

I may be confusing the purpose of this test file but personally I am using it to find examples of the ruby code that generate certain instructions. This is really helpful but the code example for the swap instruction is really complicated compared to other examples.

The added example generates much smaller number of instructions:

ruby --dump=insns -e "defined? [[]]"

== disasm: #<ISeq:<main>@-e:1 (1,0)-(1,13)> (catch: TRUE)
== catch table
| catch type: rescue st: 0001 ed: 0003 sp: 0000 cont: 0005
| == disasm: #<ISeq:defined guard in <main>@-e:0 (0,0)-(-1,-1)> (catch: FALSE)
| local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
| [ 1] "\#$!"@0
| 0000 putnil
| 0001 leave
|------------------------------------------------------------------------
0000 putnil                                                           (   1)[Li]
0001 putobject                    "expression"
0003 swap
0004 pop
0005 leave

I'm keeping the existing example because for my purposes the more examples we have - the better 🙃

[ko1]

We can merge this PR but I think it seems fragile (some optimizations can remove these instructions).