No ERB templates of YAML needed at this point

Reminded myself that "on" is Boolean in YAML and Psych intentionally
dumps it as "'on':".

https://yaml.org/type/bool.html
https://github.com/ruby/psych/blob/587c50f91421ae51059753a25357a4c42ab685f5/lib/psych/visitors/yaml_tree.rb#L281-L283
https://github.com/ruby/psych/blob/587c50f91421ae51059753a25357a4c42ab685f5/lib/psych/scalar_scanner.rb#L50-L51

Thus intentionally generating boolean, as in GA docs:
https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#on

support/ci/generate

@@ -3,7 +3,6 @@
 # frozen_string_literal: true
 
 require "bundler/inline"
-require "erb"
 require "psych"
 
 gemfile do
@@ -813,12 +812,14 @@ class CI
 
       File.write(
         File.join(workflows_root, filename),
-        ERB.new(
-          File.read(File.join(template_root, "template.yaml.erb"))
-        ).result_with_hash(
-          name: name,
-          on: as_formatted_yaml(gem.fetch(:on).reduce(&:merge), indent: 2),
-          job: as_formatted_yaml({ gem.fetch(:job_name) => job }, indent: 2)
+        as_formatted_yaml(
+          {
+            "name" => name,
+            "on" => gem.fetch(:on).reduce(&:merge),
+            "jobs" => {
+              gem.fetch(:job_name) => job
+            }
+          }
         )
       )
 
@@ -836,13 +837,14 @@ class CI
       end
   end
 
-  def as_formatted_yaml(content, indent:)
+  def as_formatted_yaml(content)
     Psych
       .safe_dump(content, line_width: 120)
       .lines
       .drop(1)
-      .join(" " * indent)
+      .join
       .strip
+      .gsub(/'on':\n/, "on:\n")
   end
 
   def initialize(workflows_root, template_root)