data race in http_backend.go:190

[For-ACGN]

==================
WARNING: DATA RACE
Write at 0x00c0000984d8 by goroutine 31:
  github.com/gocolly/colly/v2.(*httpBackend).Do()
      github.com/gocolly/colly/v2@v2.1.1-0.20210315141944-34f9af5d9113/http_backend.go:190 +0x96f
  github.com/gocolly/colly/v2.(*httpBackend).Cache()
      github.com/gocolly/colly/v2@v2.1.1-0.20210315141944-34f9af5d9113/http_backend.go:134 +0xad
  github.com/gocolly/colly/v2.(*Collector).fetch()
      github.com/gocolly/colly/v2@v2.1.1-0.20210315141944-34f9af5d9113/colly.go:675 +0x559

Previous read at 0x00c0000984d8 by goroutine 39:
  net/http.(*persistConn).readLoop()
      net/http/transport.go:2214 +0xd6b

Goroutine 31 (running) created at:
  github.com/gocolly/colly/v2.(*Collector).scrape()
      github.com/gocolly/colly/v2@v2.1.1-0.20210315141944-34f9af5d9113/colly.go:593 +0x778
  github.com/gocolly/colly/v2.(*Collector).Visit()
      github.com/gocolly/colly/v2@v2.1.1-0.20210315141944-34f9af5d9113/colly.go:459 +0xcc
  project/temp.TestGoColly()
      project/temp/temp_test.go:865 +0x75d
  testing.tRunner()
      testing/testing.go:1194 +0x202

Goroutine 39 (running) created at:
  net/http.(*Transport).dialConn()
      net/http/transport.go:1743 +0xc2b
  net/http.(*Transport).dialConnFor()
      net/http/transport.go:1442 +0x165
==================

commit where the code first appears

[WGH-]

I wish you attached a code to reproduce it... because existing tests never trigger the bug even though we're using race detector in CI test runs. Using http.Client without a timeout set seems to be a requirement to trigger the bug (which Colly doesn't do by default).