Update test-requirements-2.txt

Author: Sovietaced

opentelemetry-proto/test-requirements-2.txt

@@ -6,7 +6,7 @@ importlib-metadata==6.11.0
 iniconfig==2.0.0
 packaging==23.2
 pluggy==1.4.0
-protobuf==5.27.0
+protobuf==5.26.0
 py==1.11.0
 py-cpuinfo==9.0.0
 pytest==7.1.3