test(carvel): add structured variable to sample-tile for round-trip coverage

Updates testdata/sample-tile/base.yml from variables: [] to a real
certificate variable declaration, and updates the "populates the output
metadata" integration test to assert the variable is preserved through
the bake process.

TNZ-112157

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: drich10

internal/carvel/baker_test.go

@@ -170,7 +170,9 @@ var _ = Describe("Carvel Baker", func() {
 					Expect(outMeta.Serial).To(BeFalse())
 					Expect(outMeta.PropertyBlueprints).To(HaveLen(2))
 					Expect(outMeta.FormTypes).To(HaveLen(1))
-					Expect(outMeta.Variables).To(BeEmpty())
+					Expect(outMeta.Variables).To(HaveLen(1))
+				Expect(outMeta.Variables[0].Name).To(Equal("sample-tile-ca"))
+				Expect(outMeta.Variables[0].Type).To(Equal("certificate"))
 					Expect(outMeta.Releases).To(HaveLen(1))
 					Expect(outMeta.Releases[0]).To(ContainSubstring("k8s-tile-test"))
 					Expect(outMeta.InstanceGroups).To(HaveLen(0))

internal/carvel/testdata/sample-tile/base.yml

@@ -11,7 +11,13 @@ property_blueprints:
 - $( property "admin_password" )
 form_types:
 - $( form "db_props" )
-variables: []
+variables:
+- name: sample-tile-ca
+  type: certificate
+  options:
+    common_name: Sample Tile CA
+    is_ca: true
+    duration: 730
 package_installs:
 - $( package "test-install" )
 compatible_kubernetes_distributions: