Downgrade log injection precision to medium

This is in line with the precision of this query for other languages

Author: mbg

go/ql/src/Security/CWE-117/LogInjection.ql

@@ -5,7 +5,7 @@
  * @kind path-problem
  * @problem.severity error
  * @security-severity 7.8
- * @precision high
+ * @precision medium
  * @id go/log-injection
  * @tags security
  *       external/cwe/cwe-117