[FIX] decode headers with latin1

[bojiang]

Description

ref: benoitc/gunicorn#1778

Motivation and Context

How Has This Been Tested?

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature and improvements (non-breaking change which adds/improves functionality)
• Bug fix (non-breaking change which fixes an issue)
• Code Refactoring (internal change which is not user facing)
• Documentation
• Test, CI, or build

Component(s) if applicable

• BentoService (service definition, dependency management, API input/output adapters)
• Model Artifact (model serialization, multi-framework support)
• Model Server (mico-batching, dockerisation, logging, OpenAPI, instruments)
• YataiService gRPC server (model registry, cloud deployment automation)
• YataiService web server (nodejs HTTP server and web UI)
• Internal (BentoML's own configuration, logging, utility, exception handling)
• BentoML CLI

Checklist:

• My code follows the bentoml code style, both ./dev/format.sh and
  ./dev/lint.sh script have passed
  (instructions).
• My change reduces project test coverage and requires unit tests to be added
• I have added unit tests covering my code change
• My change requires a change to the documentation
• I have updated the documentation accordingly

[codecov]

Codecov Report

Merging #864 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #864   +/-   ##
=======================================
  Coverage   60.69%   60.70%           
=======================================
  Files         118      118           
  Lines        7959     7960    +1     
=======================================
+ Hits         4831     4832    +1     
  Misses       3128     3128           

Impacted Files	Coverage Δ
bentoml/adapters/dataframe_input.py	74.07% <ø> (ø)
bentoml/adapters/base_input.py	84.21% <100.00%> (ø)
bentoml/marshal/utils.py	60.81% <100.00%> (+0.53%)	⬆️

---

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 0846b6b...77f291a. Read the comment docs.