Update is_binaryop_nestable to retain the same meaning on JuliaSyntax@1

[penelopeysm]

Closes #1013

f() = ... used to return true for is_assignment(cst) with JuliaSyntax@0.4

 julia> parseall(GreenNode, s)
       1:153    │[toplevel]
       1:153    │  [=]
       1:103    │    [::]
       1:97     │      [call]
       1:17     │        Identifier       ✔
      18:18     │        (
      19:70     │        [::]
      19:20     │          Identifier     ✔
      21:22     │          ::
      23:70     │          [curly]
      23:27     │            Identifier   ✔
      28:28     │            {
      29:46     │            Identifier   ✔
      47:47     │            ,
      48:69     │            Identifier   ✔
      70:70     │            }
      71:71     │        ,
      72:72     │        Whitespace
      73:96     │        [::]
      73:79     │          Identifier     ✔
      80:81     │          ::
      82:96     │          Identifier     ✔
      97:97     │        )
      98:99     │      ::
     100:103    │      Identifier         ✔
     104:104    │    Whitespace
     105:105    │    =
     106:106    │    Whitespace
     107:153    │    [call]
     107:123    │      Identifier         ✔
     124:124    │      (
     125:126    │      Identifier         ✔
     127:127    │      ,
     128:128    │      Whitespace
     129:135    │      Identifier         ✔
     136:136    │      ,
     137:137    │      Whitespace
     138:152    │      [.]
     138:144    │        Identifier       ✔
     145:145    │        .
     146:152    │        [quote]
     146:152    │          Identifier
     153:153    │      )

But it's different in JuliaSyntax v1

     1:154    │[toplevel]
     1:153    │  [function]
     1:103    │    [::]
     1:97     │      [call]
     1:17     │        Identifier       ✔
    18:18     │        (
    19:70     │        [::]
    19:20     │          Identifier     ✔
    21:22     │          ::
    23:70     │          [curly]
    23:27     │            Identifier   ✔
    28:28     │            {
    29:46     │            Identifier   ✔
    47:47     │            ,
    48:69     │            Identifier   ✔
    70:70     │            }
    71:71     │        ,
    72:72     │        Whitespace
    73:96     │        [::]
    73:79     │          Identifier     ✔
    80:81     │          ::
    82:96     │          Identifier     ✔
    97:97     │        )
    98:99     │      ::
   100:103    │      Identifier         ✔
   104:104    │    Whitespace
   105:105    │    =
   106:106    │    Whitespace
   107:153    │    [call]
   107:123    │      Identifier         ✔
   124:124    │      (
   125:126    │      Identifier         ✔
   127:127    │      ,
   128:128    │      Whitespace
   129:135    │      Identifier         ✔
   136:136    │      ,
   137:137    │      Whitespace
   138:152    │      [.]
   138:144    │        Identifier       ✔
   145:145    │        .
   146:152    │        Identifier       ✔
   153:153    │      )
   154:154    │  NewlineWs

which causes is_assignment() to return false. The solution is to add defines_function(cst) to catch this case.

[github-actions]

Docs preview for PR #1193

[penelopeysm]

This broke #911

[6](https://github.com/JuliaEditorSupport/JuliaFormatter.jl/actions/runs/28249996807/job/83698800525?pr=1193#step:6:149)
Formatting output did not match expected value.

Expected:
@testset begin
    DynamicPPL.assume(
        ::Random.AbstractRNG, ::DynamicPPL.Sampler{MyEmptyAlg}, dist, vn, vi
    ) = DynamicPPL.assume(dist, vn, vi)
end


Got:
@testset begin
    DynamicPPL.assume(::Random.AbstractRNG, ::DynamicPPL.Sampler{MyEmptyAlg}, dist, vn, vi) = DynamicPPL.assume(
        dist, vn, vi
    )
end


Repro:
s = "@testset begin\n    DynamicPPL.assume(::Random.AbstractRNG, ::DynamicPPL.Sampler{MyEmptyAlg}, dist, vn, vi) = DynamicPPL.assume(\n            dist, vn, vi\n        )\nend\n"
format_text(s, BlueStyle())
911: Test Failed at /home/runner/work/JuliaFormatter.jl/JuliaFormatter.jl/src/internal/utils.jl:211