Change function position within impl

[lms0806]

The modification changed the function position within impl to be the same as the characteristic.

[codecov]

Codecov Report

❌ Patch coverage is 51.20482% with 81 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.60%. Comparing base (0f4ca67) to head (0e7ea4b).

Files with missing lines	Patch %	Lines
serde_with/src/content/de.rs	25.92%	40 Missing ⚠️
serde_with/src/enum_map.rs	0.00%	15 Missing ⚠️
serde_with/src/key_value_map.rs	34.78%	15 Missing ⚠️
serde_with/src/flatten_maybe.rs	27.27%	8 Missing ⚠️
serde_with/src/content/ser.rs	50.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #968   +/-   ##
=======================================
  Coverage   68.60%   68.60%           
=======================================
  Files          37       37           
  Lines        9784     9784           
=======================================
  Hits         6712     6712           
  Misses       3072     3072           

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