Introduce a test_ci_launcher job

[cottsay]

This can be used to validate infrastructure changes that might impact the launcher job.

The job template previously re-computed the downstream job names for predicting the build numbers, but this change re-uses the job names that are passed to the template to begin with, which is probably the right thing to do anyway.

[cottsay]

Here's the diff for the groovy in ci_launcher:

@@ -200,6 +200,6 @@
-build_numbers = [:]
-build_numbers["linux"] = predict_build_number("ci_linux")
-build_numbers["linux-aarch64"] = predict_build_number("ci_linux-aarch64")
-build_numbers["windows"] = predict_build_number("ci_windows")
-
-for (item in build_numbers) {
+predicted_jobs = [:]
+predicted_jobs["linux"] = new Tuple("ci_linux", predict_build_number("ci_linux"))
+predicted_jobs["linux-aarch64"] = new Tuple("ci_linux-aarch64", predict_build_number("ci_linux-aarch64"))
+predicted_jobs["windows"] = new Tuple("ci_windows", predict_build_number("ci_windows"))
+
+for (item in predicted_jobs) {
@@ -210,2 +210,2 @@
-  job_name = "ci_${item.key}"
-  build_number = item.value
+  job_name = item.value[0]
+  build_number = item.value[1]

Here's the first invocation of the new test_ci_launcher job: https://ci.ros2.org/view/All/job/test_ci_launcher/1/

[cottsay]

This has been deployed.