build: bump to go 1.21.3 (#18717)

Go 1.21.3 fixes an important HTTP2 CVE (see CVE-2023-39325 and
CVE-2023-44487). Nomad does not use HTTP2 and is not vulnerable. However we
should pick up the toolchain bump if for no other reason than we don't have to
answer questions about that.

.changelog/18717.txt

@@ -0,0 +1,3 @@
+```release-note:security
+build: Update to Go 1.21.3
+```

.go-version

@@ -1 +1 @@
-1.21.0
+1.21.3

contributing/README.md

@@ -30,7 +30,7 @@ A development environment is supplied via Vagrant to make getting started easier
 
 Developing without Vagrant
 ---
-1. Install [Go 1.21.0+](https://golang.org/) *(Note: `gcc-go` is not supported)*
+1. Install [Go 1.21.3+](https://golang.org/) *(Note: `gcc-go` is not supported)*
 1. Clone this repo
    ```sh
    $ git clone https://github.com/hashicorp/nomad.git

scripts/linux-priv-go.sh

@@ -21,7 +21,7 @@ case $(arch) in
 esac
 
 function install_go() {
-	local go_version="1.21.0"
+	local go_version="1.21.3"
 	local download="https://storage.googleapis.com/golang/go${go_version}.linux-${ARCH}.tar.gz"
 
 	if go version 2>&1 | grep -q "${go_version}"; then

scripts/release/mac-remote-build

@@ -56,7 +56,7 @@ REPO_PATH="${TMP_WORKSPACE}/gopath/src/github.com/hashicorp/nomad"
 mkdir -p "${TMP_WORKSPACE}/tmp"
 
 install_go() {
-  local go_version="1.21.0"
+  local go_version="1.21.3"
   local download=
 
   download="https://storage.googleapis.com/golang/go${go_version}.darwin-amd64.tar.gz"