main.star: make 1.19 and 1.20 TOOLS_GO_BRANCHES trybots optional

We still want to be able to trigger them in the very immediate future,
but they don't need to be included by default and block submission.

For golang/go#65917.

Change-Id: I2d8d0602c631bd7335488c4c473081812fc07dde
Reviewed-on: https://go-review.googlesource.com/c/build/+/610395
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

generated/commit-queue.cfg

@@ -77548,10 +77548,12 @@ config_groups {
       }
       builders {
         name: "golang/try/x_tools-go1.19-linux-amd64"
+        includable_only: true
         disable_reuse: true
       }
       builders {
         name: "golang/try/x_tools-go1.20-linux-amd64"
+        includable_only: true
         disable_reuse: true
       }
       builders {

main.star

@@ -563,9 +563,9 @@ INTERNAL_GO_BRANCHES = {
 #
 # This is planned to be removed soon after Go 1.23.0 per go.dev/issue/65917.
 TOOLS_GO_BRANCHES = {
-    "go1.21": struct(branch = "release-branch.go1.21", bootstrap = "1.17.13"),
-    "go1.20": struct(branch = "release-branch.go1.20", bootstrap = "1.17.13"),
-    "go1.19": struct(branch = "release-branch.go1.19", bootstrap = "1.17.13"),
+    "go1.21": struct(branch = "release-branch.go1.21", bootstrap = "1.17.13", optional_only = False),
+    "go1.20": struct(branch = "release-branch.go1.20", bootstrap = "1.17.13", optional_only = True),
+    "go1.19": struct(branch = "release-branch.go1.19", bootstrap = "1.17.13", optional_only = True),
 }
 
 # We set build priorities by environment. These should always be lower than the
@@ -2046,6 +2046,7 @@ def _define_go_ci():
                     luci.cq_tryjob_verifier(
                         builder = try_builder,
                         cq_group = cq_group.name,
+                        includable_only = TOOLS_GO_BRANCHES[extra_go_release].optional_only,
                         disable_reuse = True,
                     )