Adopt to gabbi 4.0.0

gabbi 4.0.0 replaced the urllib library by the httpx library, which
encodes response body by utf-8 by default. Update the assertion of
response bodies which contain unicode characters.

FIPs job is made non-voting because we need [1] to fix it.

[1] https://review.opendev.org/c/openstack/ceilometer/+/978865

Change-Id: I0a5b89020c3a7b91dae5eef3c52c6ac7856883ab
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>
diff --git a/requirements.txt b/requirements.txt
index 6a74e48..6c829a9 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,6 +2,6 @@
 oslo.config>=6.0.0 # Apache-2.0
 oslo.utils>=3.37.0 # Apache-2.0
 tempest>=17.1.0 # Apache-2.0
-gabbi>=2.7.0 # Apache-2.0
+gabbi>=4.0.0 # Apache-2.0
 requests>=2.14.2 # Apache-2.0
 testtools>=2.2.0 # MIT