PY: add missing security tags on Python queries

python/ql/src/Security/CWE-730/PolynomialReDoS.ql

@@ -4,6 +4,7 @@
  *              to match may be vulnerable to denial-of-service attacks.
  * @kind path-problem
  * @problem.severity warning
+ * @security-severity 7.5
  * @precision high
  * @id py/polynomial-redos
  * @tags security

python/ql/src/Security/CWE-730/ReDoS.ql

@@ -5,6 +5,7 @@
  *              attacks.
  * @kind problem
  * @problem.severity error
+ * @security-severity 7.5
  * @precision high
  * @id py/redos
  * @tags security

python/ql/src/Security/CWE-730/RegexInjection.ql

@@ -5,6 +5,7 @@
  *              exponential time on certain inputs.
  * @kind path-problem
  * @problem.severity error
+ * @security-severity 7.5
  * @precision high
  * @id py/regex-injection
  * @tags security