fix(gitlab-ci-config): allow strings in the 'include' keyword

This fix is a followup to !24098 which introduced a validation of the
`include:` keyword of a gitlab-ci configuration file when triggered
from /ci/lint API calls.

However, there was a test case missing: the case of a single string as
value. I have added a test case for that which shows that the code was
not validating it correctly.

This commit fixes that to allow all `include:` valid inputs.

1 files changed, 8 insertions, 0 deletions

diff --git a/spec/lib/gitlab/ci/yaml_processor_spec.rb b/spec/lib/gitlab/ci/yaml_processor_spec.rb
index 63a0d54dcfc..8b39c4e4dd0 100644
--- a/spec/lib/gitlab/ci/yaml_processor_spec.rb
+++ b/spec/lib/gitlab/ci/yaml_processor_spec.rb
@@ -615,6 +615,14 @@ module Gitlab
         subject { Gitlab::Ci::YamlProcessor.new(YAML.dump(config), opts) }
 
         context "when validating a ci config file with no project context" do
+          context "when a single string is provided" do
+            let(:include_content) { "/local.gitlab-ci.yml" }
+
+            it "does not return any error" do
+              expect { subject }.not_to raise_error
+            end
+          end
+
           context "when an array is provided" do
             let(:include_content) { ["/local.gitlab-ci.yml"] }