fix:s3 handler ,cat function decode exception

[dualc]

What does this PR do?

undecoded is byte, which can't concatenate with str type, so fix some type mismatch err in cat function
fix issue #820

[Borda]

Could we pls add some tests?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.13%. Comparing base (cb2eb37) to head (b979d54).
⚠️ Report is 22 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #821      +/-   ##
==========================================
- Coverage   91.54%   91.13%   -0.42%     
==========================================
  Files          17       17              
  Lines        1621     1635      +14     
==========================================
+ Hits         1484     1490       +6     
- Misses        137      145       +8     

Files with missing lines	Coverage Δ
papermill/s3.py	78.17% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[dualc]

Could we pls add some tests?

ok,I have added test