build: go 1.24

We were running behind and there were quite some deprecations to update.
This was mostly in the upstream copy/pasta package but seems quite
minimal.

vendor/google.golang.org/grpc/internal/envconfig/envconfig.go

@@ -49,7 +49,7 @@ var (
 	// XDSFallbackSupport is the env variable that controls whether support for
 	// xDS fallback is turned on. If this is unset or is false, only the first
 	// xDS server in the list of server configs will be used.
-	XDSFallbackSupport = boolFromEnv("GRPC_EXPERIMENTAL_XDS_FALLBACK", false)
+	XDSFallbackSupport = boolFromEnv("GRPC_EXPERIMENTAL_XDS_FALLBACK", true)
 	// NewPickFirstEnabled is set if the new pickfirst leaf policy is to be used
 	// instead of the exiting pickfirst implementation. This can be enabled by
 	// setting the environment variable "GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST"

vendor/google.golang.org/grpc/internal/envconfig/xds.go

@@ -53,4 +53,14 @@ var (
 
 	// C2PResolverTestOnlyTrafficDirectorURI is the TD URI for testing.
 	C2PResolverTestOnlyTrafficDirectorURI = os.Getenv("GRPC_TEST_ONLY_GOOGLE_C2P_RESOLVER_TRAFFIC_DIRECTOR_URI")
+
+	// XDSDualstackEndpointsEnabled is true if gRPC should read the
+	// "additional addresses" in the xDS endpoint resource.
+	XDSDualstackEndpointsEnabled = boolFromEnv("GRPC_EXPERIMENTAL_XDS_DUALSTACK_ENDPOINTS", true)
+
+	// XDSSystemRootCertsEnabled is true when xDS enabled gRPC clients can use
+	// the system's default root certificates for TLS certificate validation.
+	// For more details, see:
+	// https://github.com/grpc/proposal/blob/master/A82-xds-system-root-certs.md.
+	XDSSystemRootCertsEnabled = boolFromEnv("GRPC_EXPERIMENTAL_XDS_SYSTEM_ROOT_CERTS", false)
 )