GetCapabilities: set HighApiVersion to 2.3

The latest version of Remote APIs is v2.3.

Let's make sure that we follow the specification and avoid future v2.4
or v3.0 clients to try using our API before we support it.

server/remote_cache/capabilities_server/capabilities_server.go

@@ -15,9 +15,7 @@ import (
 	remote_cache_config "github.com/buildbuddy-io/buildbuddy/server/remote_cache/config"
 )
 
-var (
-	bazel6 = bazel_request.MustParseVersion("6.0.0")
-)
+var bazel6 = bazel_request.MustParseVersion("6.0.0")
 
 type CapabilitiesServer struct {
 	env environment.Env
@@ -50,9 +48,9 @@ func NewCapabilitiesServer(env environment.Env, supportCAS, supportRemoteExec, s
 
 func (s *CapabilitiesServer) GetCapabilities(ctx context.Context, req *repb.GetCapabilitiesRequest) (*repb.ServerCapabilities, error) {
 	c := repb.ServerCapabilities{
-		// Support bazel 2.0 -> 99.9
+		// Support bazel 2.0 -> 2.3
 		LowApiVersion:  &smpb.SemVer{Major: int32(2)},
-		HighApiVersion: &smpb.SemVer{Major: int32(99), Minor: int32(9)},
+		HighApiVersion: &smpb.SemVer{Major: int32(2), Minor: int32(3)},
 	}
 	var compressors []repb.Compressor_Value
 	if s.supportZstd {