[GR-64701] Re-parse graphs in OptimizeLongJumpsTest.

[graalvmbot]

The OptimizeLongJumpsTest checks the number of jmp/jcc in raw machine code.
In rare circumstances, constants (e.g., displacements) in the code can look like opcodes for jmp/jcc which can transiently fail the test.
To avoid this, the code is emitted again in such cases (up to three times) as it is unlikely that such constants are present multiple times in a row.
However, emitting the code again also requires the graph to be parsed again.
Otherwise, the graph will already be in an unexpected state when doing the second code emit.