Actions: Add security-severity to excessive secrets exposure query

Same value as missing actions permissions,
both providing warnings to follow the
principle of least privilege within a
workflow.

actions/ql/src/Security/CWE-312/ExcessiveSecretsExposure.ql

@@ -3,6 +3,7 @@
  * @description All organization and repository secrets are passed to the workflow runner.
  * @kind problem
  * @precision high
+ * @security-severity 5.0
  * @problem.severity warning
  * @id actions/excessive-secrets-exposure
  * @tags actions