ci: Fix comment formatting for list of vulnerable packages

When formatting the comment containing the list of vulnerable packages
for the PR, we accidentally overwrite the content of the "body"
variable, which results in the HTML tags being lost, and the full table
being always displayed (instead of hidden in a "<details>" block). Let's
fix it.

Fixes: da0cf47 ("Clean up SBOM")
Signed-off-by: Quentin Monnet <qmo@qmon.net>

Author: qmonnet

.github/workflows/build.yml

@@ -178,7 +178,7 @@ jobs:
             let fs = require('fs');
             let body = "<details>\n";
             body += "<summary>\n\n";
-            body = "## Vulnerable packages (gnu64):\n";
+            body += "## Vulnerable packages (gnu64):\n";
             body += "</summary>\n\n";
             body += fs.readFileSync('/tmp/dpdk-sys/builds/env.sysroot.gnu64.vulns.triage.md');
             body += "\n</details>\n";