CI: Apply shfmt check

Author: ChinYikMing

.github/workflows/main.yml

@@ -505,7 +505,7 @@ jobs:
     - uses: actions/checkout@v4
     - name: coding convention
       run: |
-            sudo apt-get install -q=2 clang-format-18
+            sudo apt-get install -q=2 clang-format-18 shfmt
             .ci/check-newline.sh
             .ci/check-format.sh
       shell: bash