Call on_chunk_sent when write_eof is called with a valid chunk

[pfreixes]

What do these changes do?

Fixes a bug with on_chunk_sent signal that must be triggered when write_eof is called using a valid chunk.

Related issue number

#2909

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[codecov-io]

Codecov Report

Merging #2911 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2911      +/-   ##
==========================================
+ Coverage   97.98%   97.98%   +<.01%     
==========================================
  Files          40       40              
  Lines        7506     7508       +2     
  Branches     1316     1317       +1     
==========================================
+ Hits         7355     7357       +2     
  Misses         48       48              
  Partials      103      103

Impacted Files	Coverage Δ
aiohttp/http_writer.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2584ba2...2e372cd. Read the comment docs.

[asvetlov]

Please merge.
Would you [backport] the PR to 3.1 branch?

[pfreixes]

Yes, I will make the backport.