When running build_registry.go multiple times, we hit resource not modified http error 304

Describe the bug
With code generation check worflow, we run build_registry.go multiple times in quick succession. During its run, we do http.get on https://www.iana.org/assignments/ipfix/ipfix-information-elements.csv. There is cache control introduced on this link/resource, so we hit the error 304. Because of this error, we generate empty pkg/registry/registry_IANA.go file.
In addition, because of this code generation check workflow fails on PRs.

To Reproduce
Run the following commands multiple times in quick succession:
go run pkg/registry/build_registry/build_registry.go

Expected behavior
Even with multiple runs of build_registry.go, we should see proper generation of the file, pkg/registry/registry_IANA.go with all the info elements in it.

Actual Behavior
Because of this HTTP error, we generate empty go file.

Versions
master branch ToT.

Additional context
Add any other context about the problem here.

Start with pkg/registry/build_registry/build_registry.go and run go run pkg/registry/build_registry/build_registry.go repeatedly to observe the HTTP 304 failure. Trace how the response is handled before writing pkg/registry/registry_IANA.go. Done means repeated runs produce a populated registry_IANA.go file and the code-generation check no longer fails.