Swift: Upgrade two queries to @precision high.

Author: geoffw0

swift/ql/src/queries/Security/CWE-311/CleartextStorageDatabase.ql

@@ -5,7 +5,7 @@
  * @kind path-problem
  * @problem.severity warning
  * @security-severity 7.5
- * @precision medium
+ * @precision high
  * @id swift/cleartext-storage-database
  * @tags security
  *       external/cwe/cwe-312

swift/ql/src/queries/Security/CWE-312/CleartextStoragePreferences.ql

@@ -4,7 +4,7 @@
  * @kind path-problem
  * @problem.severity warning
  * @security-severity 7.5
- * @precision medium
+ * @precision high
  * @id swift/cleartext-storage-preferences
  * @tags security
  *       external/cwe/cwe-312