chore: Remove restriction that protobuf should be less than 5 (#1193)

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

pytest.ini

@@ -17,4 +17,6 @@ filterwarnings =
     # Added to suppress "DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html"
     # Remove once the minimum supported version of googleapis-common-protos is 1.62.0
     ignore:.*pkg_resources.declare_namespace:DeprecationWarning
-    ignore:.*pkg_resources is deprecated as an API:DeprecationWarning
+    ignore:.*pkg_resources is deprecated as an API:DeprecationWarning
+    # Remove once https://github.com/googleapis/python-pubsub/issues/1206 is fixed.
+    ignore:.*connections\(\) is deprecated and will be removed; use net_connections\(\) instead:DeprecationWarning

setup.py

@@ -42,7 +42,7 @@
     "google-api-core[grpc] >= 1.34.0, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.*,!=2.4.*,!=2.5.*,!=2.6.*,!=2.7.*,!=2.8.*,!=2.9.*,!=2.10.*",
     "proto-plus >= 1.22.0, <2.0.0dev",
     "proto-plus >= 1.22.2, <2.0.0dev; python_version>='3.11'",
-    "protobuf>=3.19.5,<5.0.0dev,!=3.20.0,!=3.20.1,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
+    "protobuf>=3.20.2,<6.0.0dev,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
     "grpc-google-iam-v1 >= 0.12.4, < 1.0.0dev",
     "grpcio-status >= 1.33.2",
 ]

testing/constraints-3.7.txt

@@ -7,7 +7,7 @@
 google-api-core==1.34.0
 google-auth==2.14.1
 proto-plus==1.22.0
-protobuf==3.19.5
+protobuf==3.20.2
 grpc-google-iam-v1==0.12.4
 grpcio==1.51.3
 grpcio-status==1.33.2