windows-check: Print config.log on mingw-regress failure

The mingw-regress job's wolfssh configure step fails with
"libwolfssl is required for wolfssh" even though libwolfssl.a is
installed at the expected path. AC_CHECK_LIB only reports pass/fail;
dump config.log on failure to see the actual link error.

.github/workflows/windows-check.yml

@@ -294,3 +294,8 @@ jobs:
         make -j$(nproc) tests/regress.test tests/unit.test
         ./tests/regress.test
         ./tests/unit.test
+
+    - name: Show config.log on failure
+      if: failure()
+      working-directory: wolfssh
+      run: cat config.log