logs: use %o to format error

otherwise, they are printed as multi-line and this messes up tail+date formatting

src/platform.js

@@ -105,7 +105,7 @@ async function pruneInfraImages() {
     for (const image of images) {
         const output = safe.child_process.execSync(`docker images --digests ${image.repo} --format "{{.ID}} {{.Repository}}:{{.Tag}}@{{.Digest}}"`, { encoding: 'utf8' });
         if (output === null) {
-            debug(`Failed to list images of ${image}`, safe.error);
+            debug(`Failed to list images of ${image}. %o`, safe.error);
             throw safe.error;
         }