Bump versions.grpc from 1.66.0 to 1.68.0

Bumps `versions.grpc` from 1.66.0 to 1.68.0.

Updates `io.grpc:grpc-bom` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](https://github.com/grpc/grpc-java/commits)

Updates `io.grpc:protoc-gen-grpc-java` from 1.66.0 to 1.68.0
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](https://github.com/grpc/grpc-java/commits)

---
updated-dependencies:
- dependency-name: io.grpc:grpc-bom
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: io.grpc:protoc-gen-grpc-java
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

build.gradle

@@ -35,7 +35,7 @@ allprojects {
   ext {
     versions = [
       wiremock: "3.9.1",
-      grpc    : "1.66.0",
+      grpc    : "1.68.0",
       protobuf: "3.25.5"
     ]