Unable to use patched version of grpcio with google-cloud-pubsub

[cglewis]

There are a number of bugs (functionally and security wise) in grpcio < 1.63. However, >1.63 now requires >5 protobuf, but this library requires protobuf <5 making it no longer possible to install this library with a patched working version of grpcio.

Because no versions of google-cloud-pubsub match >2.21.3
 and google-cloud-pubsub (2.21.3) depends on protobuf (>=3.19.5,<3.20.0 || >3.20.0,<3.20.1 || >3.20.1,<4.21.0 || >4.21.0,<4.21.1 || >4.21.1,<4.21.2 || >4.21.2,<4.21.3 || >4.21.3,<4.21.4 || >4.21.4,<4.21.5 || >4.21.5,<5.0.0dev), google-cloud-pubsub (>=2.21.3) requires protobuf (>=3.19.5,<3.20.0 || >3.20.0,<3.20.1 || >3.20.1,<4.21.0 || >4.21.0,<4.21.1 || >4.21.1,<4.21.2 || >4.21.2,<4.21.3 || >4.21.3,<4.21.4 || >4.21.4,<4.21.5 || >4.21.5,<5.0.0dev).
Because grpcio (1.64.1) depends on protobuf (>=5.26.1,<6.0dev)
 and no versions of grpcio match >1.64.1,<2.0.0, grpcio (>=1.64.1,<2.0.0) requires protobuf (>=5.26.1,<6.0dev).
Thus, google-cloud-pubsub (>=2.21.3) is incompatible with grpcio (>=1.64.1,<2.0.0).

Can support for a newer version of protobuf be included in this library?

[mukund-ananthu]

@cglewis Thanks for creating this proposal. Raised a PR, and will check if there were any historical reasons for limiting the version to be less than 5.