[Bug-Candidate]: Phi-node print missing 'f' in f-string

[hbrodin]

Describe the issue:

When printing a Phi-node the string is not formatted.
There seems to be a 'f' missing ahead of the str in https://github.com/crytic/slither/blob/dev/slither/slithir/operations/phi.py#L36

Code example to reproduce the issue:

slither tests/complex_func.sol --print slithir-ssa

Version:

dev-branch dd91f77

Relevant log output:

Contract Increment
        Function Increment.increaseBy1()
                IRs:
                        {self.lvalue}({self.lvalue.type}) := ϕ({[str(v) for v in self._rvalues]})
                Expression: i += 1

[Boyan-MILANOV]

Closed by #1110