fix: make properties required in interface

PR-URL: #7643
Reviewed-by: Athan Reines <[email protected]>

Author: gururaj1512

lib/node_modules/@stdlib/stats/base/ztest/two-sample/results/float32/docs/types/index.d.ts

@@ -125,12 +125,12 @@ declare class ResultsStruct {
 	/**
 	* Sample mean of `x`.
 	*/
-	xmean?: number;
+	xmean: number;
 
 	/**
 	* Sample mean of `y`.
 	*/
-	ymean?: number;
+	ymean: number;
 
 	/**
 	* Test method.