Remove comments from `find_assignment_target` result

Bug report

Bug description:

Tools/cases_generator/tier1_generator.py fails if you place comment before PyStackRef_FromPyObjectNew assignment. Example reproducer (bytecodes.c:291-293):

pure inst(LOAD_CONST, (-- value)) {
     // comment
    value = PyStackRef_FromPyObjectNew(GETITEM(FRAME_CO_CONSTS, oparg));
}

/python.exe Tools/cases_generator/tier1_generator.py

Traceback (most recent call last):
  File "/Users/yyanchii/Desktop/cpython/Tools/cases_generator/tier1_generator.py", line 221, in <module>
    data = analyze_files(args.input)
  File "/Users/yyanchii/Desktop/cpython/Tools/cases_generator/analyzer.py", line 1184, in analyze_files
    return analyze_forest(parser.parse_files(filenames))
  File "/Users/yyanchii/Desktop/cpython/Tools/cases_generator/analyzer.py", line 1133, in analyze_forest
    desugar_inst(node, instructions, uops)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/yyanchii/Desktop/cpython/Tools/cases_generator/analyzer.py", line 947, in desugar_inst
    uop = make_uop("_" + inst.name, inst, op_inputs, uops)
  File "/Users/yyanchii/Desktop/cpython/Tools/cases_generator/analyzer.py", line 854, in make_uop
    deferred_refs=analyze_deferred_refs(op),
                  ~~~~~~~~~~~~~~~~~~~~~^^^^
  File "/Users/yyanchii/Desktop/cpython/Tools/cases_generator/analyzer.py", line 458, in analyze_deferred_refs
    raise analysis_error(
        "PyStackRef_FromPyObjectNew() must be assigned to an output", tkn
    )
  File "/Users/yyanchii/Desktop/cpython/Python/bytecodes.c", line 293
    
    ^
SyntaxError: PyStackRef_FromPyObjectNew() must be assigned to an output

Problem is in:
https://github.com/python/cpython/blob/22a442181d5f1ac496dac08e24fd852de404882f/Tools/cases_generator/analyzer.py#L457-L460

as lhs may contain leading comments which are ignored during extraction.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux, macOS, Windows

Linked PRs

• gh-128743

Start in Tools/cases_generator/analyzer.py around analyze_deferred_refs at lines 457-460, where the issue identifies leading comments in lhs as the cause. Reproduce with Tools/cases_generator/tier1_generator.py and the bytecodes.c example; done means a comment before the assignment no longer triggers the PyStackRef_FromPyObjectNew() error.