ci: Add error reporting

Author: KrystalDelusion

.github/workflows/test-linux.yml

@@ -170,3 +170,9 @@ jobs:
         shell: bash
         run: |
           make -j$procs test TARGETS= EXTRA_TARGETS= CONFIG=$CC
+
+      - name: Report errors
+        if: ${{ failure() }}
+        shell: bash
+        run: |
+          find tests/**/*.err -print -exec cat {} \;