Suppose YJIT runs a rb_vm_opt_send_without_block() fallback and the control frame stack looks like: ``` will_tailcall_bar [FINISH] caller_that_used_fallback ``` will_tailcall_bar() runs in the interpreter and sets up a tailcall. Right before JIT_EXEC() in the `send` instruction, the stack will look like: ``` bar [FINISH] caller_that_used_fallback ``` Previously, JIT_EXEC() ran bar() in JIT code, which caused the `FINISH` flag to return to the interpreter instead of to the JIT code running caller_that_used_fallback(), causing code to run twice and probably crash. Recent flaky failures on CI about "each stub expects a particular iseq" are probably due to leaving methods twice in `test_optimizations.rb`. Only run JIT code from the interpreter if a new frame is pushed.