go.mod: set go version to 1.22.0

The go verison was set to 1.22 but on Go versions 1.21.0 up to 1.21.10,
the toolchain upgrade logic will try to download the release "1.22",
which doesn't exist. Go 1.21.11+ incorporates CL 580217 (cherry-picked
in CL 583797) and will download 1.22.0, so it should be fine, but set
1.22.0 to allow the upgrade for users with older local toolchains.

Change-Id: I9aafaaa389ded3200b15fd3e7bb676610fa958d8
Reviewed-on: https://go-review.googlesource.com/c/mod/+/605935
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Commit-Queue: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

go.mod

@@ -1,5 +1,5 @@
 module golang.org/x/mod
 
-go 1.22
+go 1.22.0
 
 require golang.org/x/tools v0.13.0 // tagx:ignore