deps: update dependency com.google.errorprone:error_prone_annotations to v2.4.0

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
com.google.errorprone:error_prone_annotations	minor	2.3.4 -> 2.4.0

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[codecov]

Codecov Report

Merging #226 into master will increase coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #226      +/-   ##
============================================
+ Coverage     67.62%   67.72%   +0.10%     
  Complexity      384      384              
============================================
  Files            36       36              
  Lines          1986     1980       -6     
  Branches        269      267       -2     
============================================
- Hits           1343     1341       -2     
+ Misses          535      531       -4     
  Partials        108      108              

Impacted Files	Coverage Δ	Complexity Δ
.../src/main/java/com/google/cloud/AsyncPageImpl.java	64.28% <0.00%> (-2.39%)	2.00% <0.00%> (ø%)
...ud-core/src/main/java/com/google/cloud/Policy.java	92.11% <0.00%> (-0.04%)	20.00% <0.00%> (ø%)
...va/com/google/cloud/http/HttpTransportOptions.java	58.57% <0.00%> (+1.62%)	10.00% <0.00%> (ø%)
...re/src/main/java/com/google/cloud/BaseService.java	62.50% <0.00%> (+6.94%)	2.00% <0.00%> (ø%)

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