codeqlmanifest: explicitly chain to ./codeql if we have it

Author: Henning Makholm

.codeqlmanifest.json

@@ -1,3 +1,4 @@
 { "provide": [ "*/ql/src/qlpack.yml",
                "misc/legacy-support/*/qlpack.yml",
-               "misc/suite-helpers/qlpack.yml" ] }
+               "misc/suite-helpers/qlpack.yml",
+               "codeql/.codeqlmanifest.json" ] }