deps: update dependency com.google.protobuf:protobuf-bom to v3.15.1

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.google.protobuf:protobuf-bom (source)	3.15.0 -> 3.15.1

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Release Notes

protocolbuffers/protobuf

v3.15.1

Compare Source

Ruby

• Bugfix for Message.[] for repeated or map fields (#​8313)
• Fix for truncating behavior when converting Float to Duration (#​8320)

C++

• Small fixes for MinGW and for C++20 with GCC (#​8318)

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[codecov]

Codecov Report

Merging #381 (bce1834) into master (4314da9) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #381   +/-   ##
=========================================
  Coverage     67.60%   67.60%           
  Complexity      384      384           
=========================================
  Files            36       36           
  Lines          1985     1985           
  Branches        268      268           
=========================================
  Hits           1342     1342           
  Misses          535      535           
  Partials        108      108           

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