Set default Go version to 1.20 until GitLab 16.11

.gitlab-ci.yml

@@ -16,7 +16,12 @@ variables:
   TRANSFER_METER_FREQUENCY: "1s"
   DOCKER_VERSION: "20.10.15"
   BUNDLE_FROZEN: "true"
-  GO_VERSION: "golang-1.21"
+  # Due to https://go.dev/doc/toolchain, we need to keep our base image at Go 1.20
+  # until GitLab 16.11 is out which will mean we can drop support for Go 1.20
+  # and make 1.21 our minimum. Using Go 1.21 here now results in the go.mod
+  # being updated to include the 'toolchain go<version>' directive, which
+  # causes CI failures.
+  GO_VERSION: "golang-1.20"
   GOPATH: $CI_PROJECT_DIR/.GOPATH
   DEBIAN_VERSION: "bookworm"
   RUBY_VERSION: "ruby-3.2"

go.mod

 module gitlab.com/gitlab-org/gitlab-shell/v14
 
-go 1.21
-
-toolchain go1.22.1
+go 1.20
 
 require (
 	github.com/charmbracelet/git-lfs-transfer v0.1.1-0.20240308140948-6dbff1b9ed9b