deps: update dependency junit:junit to v4.13

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
junit:junit (source)	minor	4.12 -> 4.13

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[codecov]

Codecov Report

Merging #46 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master      #46      +/-   ##
============================================
- Coverage     78.85%   78.82%   -0.04%     
  Complexity      288      288              
============================================
  Files            21       21              
  Lines          2578     2578              
  Branches        128      128              
============================================
- Hits           2033     2032       -1     
  Misses          490      490              
- Partials         55       56       +1

Impacted Files	Coverage Δ	Complexity Δ
.../com/google/cloud/pubsub/v1/MessageDispatcher.java	84.61% <0%> (-0.52%)	23% <0%> (ø)

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