rebase: bump google.golang.org/grpc from 1.67.1 to 1.68.0

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.67.1 to 1.68.0.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](https://github.com/grpc/grpc-go/compare/v1.67.1...v1.68.0)

---
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>
Signed-off-by: Praveen M <m.praveen@ibm.com>

vendor/google.golang.org/grpc/mem/buffers.go

@@ -65,6 +65,9 @@ var (
 	refObjectPool    = sync.Pool{New: func() any { return new(atomic.Int32) }}
 )
 
+// IsBelowBufferPoolingThreshold returns true if the given size is less than or
+// equal to the threshold for buffer pooling. This is used to determine whether
+// to pool buffers or allocate them directly.
 func IsBelowBufferPoolingThreshold(size int) bool {
 	return size <= bufferPoolingThreshold
 }
@@ -89,7 +92,11 @@ func newBuffer() *buffer {
 //
 // Note that the backing array of the given data is not copied.
 func NewBuffer(data *[]byte, pool BufferPool) Buffer {
-	if pool == nil || IsBelowBufferPoolingThreshold(len(*data)) {
+	// Use the buffer's capacity instead of the length, otherwise buffers may
+	// not be reused under certain conditions. For example, if a large buffer
+	// is acquired from the pool, but fewer bytes than the buffering threshold
+	// are written to it, the buffer will not be returned to the pool.
+	if pool == nil || IsBelowBufferPoolingThreshold(cap(*data)) {
 		return (SliceBuffer)(*data)
 	}
 	b := newBuffer()
@@ -194,19 +201,19 @@ func (b *buffer) read(buf []byte) (int, Buffer) {
 	return n, b
 }
 
-// String returns a string representation of the buffer. May be used for
-// debugging purposes.
 func (b *buffer) String() string {
 	return fmt.Sprintf("mem.Buffer(%p, data: %p, length: %d)", b, b.ReadOnlyData(), len(b.ReadOnlyData()))
 }
 
+// ReadUnsafe reads bytes from the given Buffer into the provided slice.
+// It does not perform safety checks.
 func ReadUnsafe(dst []byte, buf Buffer) (int, Buffer) {
 	return buf.read(dst)
 }
 
 // SplitUnsafe modifies the receiver to point to the first n bytes while it
-// returns a new reference to the remaining bytes. The returned Buffer functions
-// just like a normal reference acquired using Ref().
+// returns a new reference to the remaining bytes. The returned Buffer
+// functions just like a normal reference acquired using Ref().
 func SplitUnsafe(buf Buffer, n int) (left, right Buffer) {
 	return buf.split(n)
 }
@@ -232,12 +239,21 @@ func (e emptyBuffer) read([]byte) (int, Buffer) {
 	return 0, e
 }
 
+// SliceBuffer is a Buffer implementation that wraps a byte slice. It provides
+// methods for reading, splitting, and managing the byte slice.
 type SliceBuffer []byte
 
+// ReadOnlyData returns the byte slice.
 func (s SliceBuffer) ReadOnlyData() []byte { return s }
-func (s SliceBuffer) Ref()                 {}
-func (s SliceBuffer) Free()                {}
-func (s SliceBuffer) Len() int             { return len(s) }
+
+// Ref is a noop implementation of Ref.
+func (s SliceBuffer) Ref() {}
+
+// Free is a noop implementation of Free.
+func (s SliceBuffer) Free() {}
+
+// Len is a noop implementation of Len.
+func (s SliceBuffer) Len() int { return len(s) }
 
 func (s SliceBuffer) split(n int) (left, right Buffer) {
 	return s[:n], s[n:]