Fix floats appearing in Humanize output for locales that override _format_timeframe

[anishnya]

Pull Request Checklist

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• 🧪 Added tests for changed code.
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Description of Changes

Closes #789. The issue was the locales that were overriding _format_timeframe were not truncating their output. The solution is extremely similar to #790, the difference being that we don't truncate delta on the call to _format_relative. An important note is that contributors adding new locales that override describe and describe_multi must ensure their calls to _format_timeframe have delta truncated. This might be a good note to add to #983.

[codecov]

Codecov Report

Merging #986 (b42f4c2) into master (f1df58b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #986   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2111      2111           
  Branches       333       333           
=========================================
  Hits          2111      2111           

Impacted Files	Coverage Δ
arrow/locales.py	100.00% <100.00%> (ø)

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[jadchaar]

LGTM