[ci] error in clang-format-check job

The clang-format-check job bash script part has an error where == is used instead of -eq to check the exit code of the script, the error can be seen in recent pipelines: https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/jobs/161097#L723

/usr/bin/bash: line 178: [: ==: unary operator expected