net/http/cgi: rename a test file to be less cute

My fault (from CL 4245070), sorry.

Change-Id: Ib95d3170dc326e74aa74c22421c4e44a8b00f577
Reviewed-on: https://go-review.googlesource.com/c/go/+/214920
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

diff --git a/src/net/http/cgi/matryoshka_test.go b/src/net/http/cgi/integration_test.go
similarity index 100%
rename from src/net/http/cgi/matryoshka_test.go
rename to src/net/http/cgi/integration_test.go