Update stderr files

And also fix some comments as suggested by lcnr

Author: JulianKnodt

src/test/ui/const-generics/apit-with-const-param.stderr

@@ -1,4 +1,4 @@
-// Tests that array sizes that depend on const-params does not yet work.
+// Tests that array sizes that depend on const-params are checked using `ConstEvaluatable`.
 // revisions: full min
 
 #![cfg_attr(full, feature(const_generics))]

src/test/ui/const-generics/array-size-in-generic-struct-param.rs

@@ -1,4 +1,4 @@
-// Checks whether conditions in traits can be evaluated.
+// Checks that `impl Trait<{anon_const}> for Type` evaluates successfully.
 // run-pass
 // revisions: full min