[SPARK-34951][INFRA][PYTHON][TESTS] Set the system encoding as UTF-8 to recover the Sphinx build in GitHub Actions

### What changes were proposed in this pull request?

This PR proposes to set the system encoding as UTF-8. For some reasons, it looks like GitHub Actions machines changed theirs to ASCII by default. This leads to default encoding/decoding to use ASCII in Python, e.g.) `"a".encode()`, and looks like Sphinx depends on that.

### Why are the changes needed?

To recover GItHub Actions build.

### Does this PR introduce _any_ user-facing change?

No, dev-only.

### How was this patch tested?

Tested in https://github.com/apache/spark/pull/32046

Closes #32047 from HyukjinKwon/SPARK-34951.

Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

.github/workflows/build_and_test.yml

@@ -282,6 +282,9 @@ jobs:
   lint:
     name: Linters, licenses, dependencies and documentation generation
     runs-on: ubuntu-20.04
+    env:
+      LC_ALL: C.UTF-8
+      LANG: C.UTF-8
     container:
       image: dongjoon/apache-spark-github-action-image:20201025
     steps:
@@ -357,8 +360,6 @@ jobs:
     - name: Run documentation build
       run: |
         cd docs
-        export LC_ALL=C.UTF-8
-        export LANG=C.UTF-8
         bundle exec jekyll build
 
   java-11: