build.yaml: Avoid too long code_samples_usage.diff.md

Author: adriendupuis

.github/workflows/build.yaml

@@ -186,7 +186,7 @@ jobs:
                     echo '' >> code_samples_usage.diff.md
                     php tools/code_samples/code_samples_usage_diff2html.php $HOME/code_samples_usage.diff >> code_samples_usage.diff.md
                     echo '<a href="${{ steps.artifact.outputs.artifact-url }}">Download colorized diff</a>' >> code_samples_usage.diff.md
-                    if [[ `wc -c < code_samples_usage.diff.md | xargs` -ge $((2**16)) ]]; then
+                    if [[ `wc -m < code_samples_usage.diff.md | xargs` -ge $((2**16)) ]]; then
                         echo '# code_samples/ change report' > code_samples_usage.diff.md
                         echo '' >> code_samples_usage.diff.md
                         echo 'Diff is too long to be displayed.' >> code_samples_usage.diff.md