deps: update dependency com.google.guava:guava-bom to v28.2-android

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
com.google.guava:guava-bom	minor	28.1-android -> 28.2-android

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[codecov]

Codecov Report

Merging #34 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master     #34   +/-   ##
========================================
  Coverage      66.2%   66.2%           
  Complexity       72      72           
========================================
  Files            12      12           
  Lines           432     432           
  Branches          2       2           
========================================
  Hits            286     286           
  Misses          144     144           
  Partials          2       2

Impacted Files	Coverage Δ	Complexity Δ
...cloud/texttospeech/v1beta1/TextToSpeechClient.java	58.33% <0%> (ø)	11% <0%> (ø)	⬇️
...ogle/cloud/texttospeech/v1/TextToSpeechClient.java	58.33% <0%> (ø)	11% <0%> (ø)	⬇️

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