Fix race condition in modularity test

[VeronikaSolovei9]

Possible fix for race condition in TestModulesCanBeExecutedForMultipleBiddersSimultaneously

It seems that in this test, there were two possible sources of problems:

1. There appeared to be a typo where a bidder name was duplicated.
2. bidderImpl object was shared between bidder requests.

The bidder requests are being tested in separate, concurrent goroutines, causing concurrent reads and writes to the Headers map.

The fix is to fix the typo, and to create separate objects.

One thing that is not entirely clear to me is that the Headers map is being cloned inside of the getAllBids function, and according to my investigation with breakpoints and the debug log, the error was happening in an Add method after the clone. Nonetheless, upon repeated testing, I cannot reproduce the bug after the above changes.

[VeronikaSolovei9]

I suspect something is not working as expected in func (h Header) Clone() Header { when input header in not nil and empty.

[bsardo]

The changes here look good but I think they only partially resolve the issue as I was still getting failures when running this test with race detection enabled. To fix this, I think we need to update the two mutations in mockUpdateBidRequestHook function HandleBidderRequestHook so that payload.request.Site is cloned prior to writing to Name and Domain:

c.AddMutation(
	func(payload hookstage.BidderRequestPayload) (hookstage.BidderRequestPayload, error) {
		site := ptrutil.Clone(payload.Request.Site)
		site.Name = "test"
		payload.Request.Site = site
		return payload, nil
	}, hookstage.MutationUpdate, "bidRequest", "site.name",
).AddMutation(
	func(payload hookstage.BidderRequestPayload) (hookstage.BidderRequestPayload, error) {
		site := ptrutil.Clone(payload.Request.Site)
		site.Domain = "test.com"
		payload.Request.Site = site
		return payload, nil
	}, hookstage.MutationUpdate, "bidRequest", "site.domain",
)