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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