Fix data race caused by concurrent access to the request URL during scans

[hdm]

A data race was identified when the Nuclei engine calls request.dump() when the net/http client transport for the request is still active (as part of a scan goroutine). This PR changes the Update() function to clone and replace the URL, avoiding the race. This can be tricky to reproduce (might require a HTTP/2 target) and unfortunately I misplaced the original data race log that led to this fix, but it hasn't popped up again since I made this change.

[hdm]

Doh, this is still triggering and will need more work, here's race log:

==================
WARNING: DATA RACE
Write at 0x00c064436540 by goroutine 867838:
  github.com/projectdiscovery/nuclei/v3/pkg/protocols/http.(*Request).executeRequest()
      project/nuclei/pkg/protocols/http/request.go:869 +0x7170
  github.com/projectdiscovery/nuclei/v3/pkg/protocols/http.(*Request).ExecuteWithResults.func1()
      project/nuclei/pkg/protocols/http/request.go:508 +0xa04
  github.com/projectdiscovery/nuclei/v3/pkg/protocols/http.(*Request).ExecuteWithResults()
      project/nuclei/pkg/protocols/http/request.go:585 +0x786
  github.com/projectdiscovery/nuclei/v3/pkg/tmplexec/generic.(*Generic).ExecuteWithResults()
      project/nuclei/pkg/tmplexec/generic/exec.go:61 +0x595
  github.com/projectdiscovery/nuclei/v3/pkg/tmplexec.(*TemplateExecuter).Execute()
      project/nuclei/pkg/tmplexec/exec.go:216 +0x876
  github.com/projectdiscovery/nuclei/v3/pkg/core.(*Engine).executeTemplateWithTargets.func2.1()
      project/nuclei/pkg/core/executors.go:138 +0x415
  github.com/projectdiscovery/nuclei/v3/pkg/core.(*Engine).executeTemplateWithTargets.func2.gowrap1()
      project/nuclei/pkg/core/executors.go:145 +0x61

Previous read at 0x00c064436540 by goroutine 868391:
  net/http.newTransferWriter()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/transfer.go:93 +0x3b3
  net/http.(*Request).write()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/request.go:706 +0x1011
  net/http.(*persistConn).writeLoop()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/transport.go:2593 +0x364
  net/http.(*Transport).dialConn.gowrap3()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/transport.go:1945 +0x33

Goroutine 867838 (running) created at:
  github.com/projectdiscovery/nuclei/v3/pkg/core.(*Engine).executeTemplateWithTargets.func2()
      project/nuclei/pkg/core/executors.go:114 +0xd6a
  github.com/projectdiscovery/nuclei/v3/pkg/input/provider.(*SimpleInputProvider).Iterate()
      project/nuclei/pkg/input/provider/simple.go:38 +0x8a
  github.com/projectdiscovery/nuclei/v3/pkg/core.(*Engine).executeTemplateWithTargets()
      project/nuclei/pkg/core/executors.go:79 +0x85b
  github.com/projectdiscovery/nuclei/v3/pkg/core.(*Engine).executeTemplateSpray.func1()
      project/nuclei/pkg/core/execute_options.go:137 +0x10a
  github.com/projectdiscovery/nuclei/v3/pkg/core.(*Engine).executeTemplateSpray.gowrap2()
      project/nuclei/pkg/core/execute_options.go:138 +0x41

Goroutine 868391 (running) created at:
  net/http.(*Transport).dialConn()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/transport.go:1945 +0x2dd9
  net/http.(*Transport).dialConnFor()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/transport.go:1615 +0x11d
  net/http.(*Transport).startDialConnForLocked.func1()
      /root/go/pkg/mod/golang.org/[email protected]/src/net/http/transport.go:1597 +0x3c
==================

[hdm]

This PR helps, but requires a separate PR in nuclei to resolve:

• Address race conditions in http.Request and MemGuardian nuclei#6321