rebase: bump google.golang.org/grpc from 1.68.1 to 1.69.0

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.68.1 to 1.69.0.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](https://github.com/grpc/grpc-go/compare/v1.68.1...v1.69.0)

---
updated-dependencies:
- dependency-name: google.golang.org/grpc
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/google.golang.org/grpc/preloader.go

@@ -62,7 +62,7 @@ func (p *PreparedMsg) Encode(s Stream, msg any) error {
 
 	materializedData := data.Materialize()
 	data.Free()
-	p.encodedData = mem.BufferSlice{mem.NewBuffer(&materializedData, nil)}
+	p.encodedData = mem.BufferSlice{mem.SliceBuffer(materializedData)}
 
 	// TODO: it should be possible to grab the bufferPool from the underlying
 	//  stream implementation with a type cast to its actual type (such as
@@ -76,7 +76,7 @@ func (p *PreparedMsg) Encode(s Stream, msg any) error {
 	if p.pf.isCompressed() {
 		materializedCompData := compData.Materialize()
 		compData.Free()
-		compData = mem.BufferSlice{mem.NewBuffer(&materializedCompData, nil)}
+		compData = mem.BufferSlice{mem.SliceBuffer(materializedCompData)}
 	}
 
 	p.hdr, p.payload = msgHeader(p.encodedData, compData, p.pf)