Shared: Accept the ai threat model as a source kind in model validation

ModelOutput::getAWarning reports source models whose kind is not listed in ValidSourceKind. The list did not include ai, added to the threat models in #22810, so the rows of this PR showed up as warnings in library-tests/frameworks/data.

Author: Alex-Hofer

shared/mad/codeql/mad/ModelValidation.qll

@@ -126,7 +126,7 @@ module KindValidation<KindValidationConfigSig Config> {
         [
           // shared
           "local", "remote", "file", "commandargs", "database", "environment", "reverse-dns",
-          "stdin",
+          "stdin", "ai",
           // Java
           "android-external-storage-dir", "contentprovider",
           // C#