[fix][sec] Upgrade grpc in pulsar-function-go to 1.82.1 to fix GHSA-hrxh-6v49-42gf

[lhotari]

Motivation

The Go Functions runtime module pulsar-function-go depends on google.golang.org/grpc v1.79.3, which is affected by GHSA-hrxh-6v49-42gf ("gRPC-Go: xDS RBAC and HTTP/2 Vulnerabilities", high severity). All gRPC-Go versions below 1.82.1 are affected.

The pulsar-function-go/examples module was already updated to gRPC 1.82.1 by Dependabot in #26231; this PR applies the same upgrade to the main pulsar-function-go module.

Modifications

• Upgrade google.golang.org/grpc from v1.79.3 to v1.82.1 (the first patched version for GHSA-hrxh-6v49-42gf) in pulsar-function-go/go.mod
• Transitive updates pulled in by the upgrade: google.golang.org/protobuf v1.36.10 → v1.36.11, golang.org/x/oauth2 v0.34.0 → v0.36.0, and a newer google.golang.org/genproto/googleapis/rpc snapshot
• Update go.sum accordingly

Verifying this change

• Make sure that the change passes the CI checks.

This change is already covered by existing tests: the pulsar-function-go tests run in CI. Verified locally with go build ./..., go mod verify, and go mod tidy -diff (no drift).

Does this pull request potentially affect one of the following parts:

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• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment