Configuration is never validated

[RA80533]

https://github.com/github/codeql-action/blob/f00bafbde1cf72f723cff6bcb0fa170325b2edb9/src/config-utils.ts#L1098

Unfortunately, JSON.parse() is typed as returning any. It appears that this was not an issue that was reported because noImplicitAny was explicitly disabled in the root tsconfig.json.