workhorse: replace deprecated ioutil calls

workhorse/cmd/gitlab-resize-image/png/reader.go

workhorse/cmd/gitlab-resize-image/png/reader_test.go

workhorse/config_test.go

workhorse/gitaly_test.go

workhorse/internal/api/block_test.go

workhorse/internal/artifacts/entry_test.go

workhorse/internal/badgateway/roundtripper.go

workhorse/internal/badgateway/roundtripper_test.go

workhorse/internal/git/archive.go

workhorse/internal/git/archive_test.go

workhorse/internal/git/upload-pack_test.go

workhorse/internal/helper/helpers.go

workhorse/internal/helper/tempfile.go

workhorse/internal/helper/writeafterreader.go

workhorse/internal/helper/writeafterreader_test.go

workhorse/internal/httprs/httprs.go

workhorse/internal/httprs/httprs_test.go

workhorse/internal/imageresizer/image_resizer_test.go

workhorse/internal/lsif_transformer/parser/cache.go

workhorse/internal/lsif_transformer/parser/cache_test.go