patch 9.0.0573: outdated dependencies go unnoticed

Problem:    Outdated dependencies go unnoticed.
Solution:   Use github Dependabot. (closes #11213)

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    573,
 /**/
     572,
 /**/