fix(stream): fix append_only top_n

[wcy-fdu]

What's changed and what's your intention?

As title.

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

close #3286

[codecov]

Codecov Report

Merging #3290 (b512f20) into main (d577da0) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3290      +/-   ##
==========================================
- Coverage   73.23%   73.22%   -0.01%     
==========================================
  Files         748      748              
  Lines      101766   101766              
==========================================
- Hits        74525    74523       -2     
- Misses      27241    27243       +2     

Flag	Coverage Δ
rust	73.22% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/stream/src/executor/top_n_appendonly.rs	95.07% <100.00%> (ø)
src/meta/src/barrier/mod.rs	69.94% <0.00%> (-0.30%)	⬇️
src/common/src/types/ordered_float.rs	24.70% <0.00%> (-0.20%)	⬇️

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