Update x86_64 coverage

This regression doesn't seem to be related to my change, but instead
appears to be kcov misbehaving.

Signed-off-by: Alyssa Ross <[email protected]>

Author: alyssais

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 87.7,
+  "coverage_score": 87.6,
   "exclude_path": "",
   "crate_features": ""
 }