Remove `OpenStruct` from the project (solve warnings) #290

Job	Run time
build (2.5.3, gemfiles/rails50.gemfile)	1m 6s
build (2.5.3, gemfiles/rails51.gemfile)	1m 6s
build (2.5.3, gemfiles/rails52.gemfile)	1m 10s
build (2.5.3, gemfiles/rails60.gemfile)	2m 5s
build (2.5.3, gemfiles/rails61.gemfile)	2m 18s
build (2.6.0, gemfiles/rails50.gemfile)	1m 18s
build (2.6.0, gemfiles/rails51.gemfile)	1m 7s
build (2.6.0, gemfiles/rails52.gemfile)	1m 21s
build (2.6.0, gemfiles/rails60.gemfile)	2m 17s
build (2.6.0, gemfiles/rails61.gemfile)	2m 19s
build (2.6.6, gemfiles/rails50.gemfile)	1m 11s
build (2.6.6, gemfiles/rails51.gemfile)	1m 3s
build (2.6.6, gemfiles/rails52.gemfile)	1m 16s
build (2.6.6, gemfiles/rails60.gemfile)	2m 10s
build (2.6.6, gemfiles/rails61.gemfile)	2m 14s
build (2.7.2, gemfiles/rails50.gemfile)	1m 12s
build (2.7.2, gemfiles/rails51.gemfile)	1m 5s
build (2.7.2, gemfiles/rails52.gemfile)	1m 15s
build (2.7.2, gemfiles/rails60.gemfile)	2m 14s
build (2.7.2, gemfiles/rails61.gemfile)	2m 18s
build (gemfiles/rails71.gemfile, 3.2.2)	47s
build (gemfiles/rails71.gemfile, 3.1.1)	49s
build (gemfiles/rails70.gemfile, 3.1.1)	43s
build (gemfiles/rails70.gemfile, 3.0.3)	43s
build (gemfiles/rails61.gemfile, 3.0.3)	46s
	35m 53s

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