ci: fail Lint gen on newly created files (#504)

'git diff --exit-code' only inspects tracked files, so when 'make gen'
produces new Markdown (e.g. for a new resource or data source), the
check passes while the generated file remains uncommitted.

Switch the check to 'git status --porcelain' so both modifications and
untracked output fail the step, and print the offending paths and diff
for easier debugging.

Generated by Coder Agents on behalf of @zedkipp.

Author: zedkipp

.github/workflows/test.yml

@@ -158,4 +158,9 @@ jobs:
       - name: Lint gen
         run: |
           make gen
-          git diff --exit-code
+          if [ -n "$(git status --porcelain)" ]; then
+            echo "make gen produced changes; run 'make gen' locally and commit the result:"
+            git status --porcelain
+            git --no-pager diff
+            exit 1
+          fi