Fix the JSON syntax error of running phpcd-diff action when no changes are made

[eason9487]

Changes proposed in this Pull Request:

Fix the JSON syntax error of running phpcd-diff action when no changes are made.

For some reason, if runs phpcs-diff action without any file changes, it will get a JSON syntax error because the vendor/bin/diffFilter outputs an empty result.

Detailed test instructions:

1. Create a local bash file at the repo's root directory temporality to verify the changes of this PR.

   #!/usr/bin/env bash
   JSON_REPORT="/tmp/phpcs-diff.json"
   
   # The original command
   # vendor/bin/diffFilter --phpcsStrict <(git diff HEAD^...HEAD) <(vendor/bin/phpcs ./* -q --report=json) --report=phpcs 0 > "$JSON_REPORT"
   
   # Simulate the result of no changes - an empty file.
   printf '' > "$JSON_REPORT"
   
   # Simulate the result of no PHPCS errors.
   # printf '{"files":[],"totals":{"errors":0,"fixable":0,"warnings":0}}' > "$JSON_REPORT"
   
   # Simulate the result of a PHPCS error.
   # printf '{"files":{"woocommerce-google-analytics-integration.php":{"messages":[{"message":"Expected 1 spaces before closing parenthesis; 0 found","source":"diffFilter","severity":1,"type":"ERROR","line":23,"column":1,"fixable":"false"}],"errors":1,"warnings":0}},"totals":{"errors":1,"fixable":0,"warnings":0}}' > "$JSON_REPORT"
   
   if [ ! -s "$JSON_REPORT" ]; then
     echo "No changes."
     exit 0
   fi
   
   node packages/js/github-actions/actions/phpcs-diff/src/annotate-phpcs-report.js "$JSON_REPORT"

2. Run the verification bash file with different diff results to see if the fix works well.

[tomalec]

To me it looks like a bug in diffFilter (exussum12/coverageChecker#72), as the line https://github.com/exussum12/coverageChecker/blob/495c9cb512cdb057cd2c63e6bda0efee4838bb3a/src/functions.php#L94-L95 logs an error, but does not throw, and returns with success 0 code.

IMO, it should either return 1 if the error occurred, and it cannot proper the result in a compliant format, or return the result in the compliant format (JSON)

[tomalec]

Tested locally LGTM.
💅 We may add a link to the issue in the code comment, to maybe someday be able to remove this workaround :)
(the repo is not very active, but there is always hope;) )

[eason9487]

@tomalec, thanks for reporting the issue!

We may add a link to the issue in the code comment, to maybe someday be able to remove this workaround :)

Sounds good! I added in 7d69c1e.