go/rpc: 1.21 is too new and too restrictive

project that uses it will be forced to update

go: upgraded go 1.19 => 1.21
go: added toolchain go1.21.3

which is not always disireble

Change-Id: I0878b353a7ee12371a6399894eb9b56cd3a597d9
Signed-off-by: Boris Glimcher <Boris.Glimcher@emc.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/20398


Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ben Walker <ben@nvidia.com>
Reviewed-by: Maciej Miś <maciej.mis@intel.com>
Reviewed-by: Artek Koltun <artsiom.koltun@intel.com>
Reviewed-by: Jim Harris <jim.harris@samsung.com>