ci: fix temporary file creation in tests and tighten CI check (#18374)

## Which issue does this PR close?

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- Closes #.

## Rationale for this change

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Temporary file is created during test, see reproducer in
`datafusion-cli`

```sh
yongting@Yongtings-MacBook-Pro-2 ~/C/datafusion (main=)> cargo test --package datafusion --test core_integration --all-features -- dataframe::test_copy_schema --exact --nocapture
   Compiling datafusion v50.3.0 (/Users/yongting/Code/datafusion/datafusion/core)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 2.50s
     Running tests/core_integration.rs (target/debug/deps/core_integration-dee3896b38f536b2)

running 1 test
test dataframe::test_copy_schema ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 801 filtered out; finished in 0.02s

yongting@Yongtings-MacBook-Pro-2 ~/C/datafusion (main=)> git status
On branch main
Your branch is up to date with 'upstream/main'.

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        "datafusion/core/\"/"

nothing added to commit but untracked files present (use "git add" to track)
```

This PR fixes this test, and make CI stricter for similar temporary file
creations.

## What changes are included in this PR?

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## Are these changes tested?

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Yes, I have run the CI without fix in my local repo, it's failing as
expected:
https://github.com/2010YOUY01/arrow-datafusion/actions/runs/18913128118/job/53989721867

After the fix, the CI should be able to pass.

## Are there any user-facing changes?

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Author: 2010YOUY01

.github/workflows/rust.yml

@@ -302,6 +302,15 @@ jobs:
             --features serde,avro,json,backtrace,integration-tests,parquet_encryption
       - name: Verify Working Directory Clean
         run: git diff --exit-code
+        # Check no temporary directories created during test.
+        # `false/` folder is excuded for rust cache.
+      - name: Verify Working Directory Clean (No Untracked Files)
+        run: |
+          STATUS="$(git status --porcelain | sed -e '/^?? false\/$/d' -e '/^?? false$/d')"
+          if [ -n "$STATUS" ]; then
+            echo "$STATUS"
+            exit 1
+          fi
 
   # datafusion-cli tests
   linux-test-datafusion-cli:

datafusion/core/tests/dataframe/mod.rs

@@ -6328,7 +6328,7 @@ async fn test_copy_schema() -> Result<()> {
     let target_path = tmp_dir.path().join("target.csv");
 
     let query = format!(
-        "COPY source_table TO '{:?}' STORED AS csv",
+        "COPY source_table TO '{}' STORED AS csv",
         target_path.to_str().unwrap()
     );