fix(secrev): valid SAM in doc-drift fixture templates (cfn-lint E0001)

The doc-drift sample-stack fixtures declared AWS::Serverless::Function with no
Properties; cfn-lint's SAM transform errored (HIGH). Added minimal valid
Properties (Handler/Runtime/InlineCode). Pre-existing on main — #19 pushed with
--no-verify (xargs overflow) and CI runs no cfn-lint, so it slipped through.
doc-drift still detects the stack (keys on template presence).

security-review/checkers/fixtures/doc-drift/clean-repo/template.yaml

@@ -3,3 +3,9 @@ Transform: AWS::Serverless-2016-10-31
 Resources:
   IngestFn:
     Type: AWS::Serverless::Function
+    Properties:
+      Handler: app.handler
+      Runtime: python3.12
+      InlineCode: |
+        def handler(event, context):
+            return {"statusCode": 200}

security-review/checkers/fixtures/doc-drift/drift-omits-repo/template.yaml

@@ -3,3 +3,9 @@ Transform: AWS::Serverless-2016-10-31
 Resources:
   ChargeFn:
     Type: AWS::Serverless::Function
+    Properties:
+      Handler: app.handler
+      Runtime: python3.12
+      InlineCode: |
+        def handler(event, context):
+            return {"statusCode": 200}