add additional example in the error to showcase the behavior

Author: karolzwolak

tests/ui/lint/default-groups-issue-65464.rs

@@ -8,7 +8,15 @@
 // in such tests, and the we're testing a scenario with no modification to the default settings.
 
 fn main() {
+    // additional context is provided only if the level is not explicitly set
     let WrongCase = 1;
     //~^ WARN [non_snake_case]
     //~| NOTE `#[warn(non_snake_case)]` (part of `#[warn(nonstandard_style)]`) on by default
+
+    // unchanged message if the level is explicitly set
+    // even if the level is the same as the default
+    #[warn(nonstandard_style)] //~ NOTE the lint level is defined here
+    let WrongCase = 2;
+    //~^ WARN [non_snake_case]
+    //~| NOTE `#[warn(non_snake_case)]` implied by `#[warn(nonstandard_style)]`
 }

tests/ui/lint/default-groups-issue-65464.stderr

@@ -1,10 +1,23 @@
 warning: variable `WrongCase` should have a snake case name
-  --> $DIR/default-groups-issue-65464.rs:11:9
+  --> $DIR/default-groups-issue-65464.rs:12:9
    |
 LL |     let WrongCase = 1;
    |         ^^^^^^^^^ help: convert the identifier to snake case: `wrong_case`
    |
    = note: `#[warn(non_snake_case)]` (part of `#[warn(nonstandard_style)]`) on by default
 
-warning: 1 warning emitted
+warning: variable `WrongCase` should have a snake case name
+  --> $DIR/default-groups-issue-65464.rs:19:9
+   |
+LL |     let WrongCase = 2;
+   |         ^^^^^^^^^ help: convert the identifier to snake case: `wrong_case`
+   |
+note: the lint level is defined here
+  --> $DIR/default-groups-issue-65464.rs:18:12
+   |
+LL |     #[warn(nonstandard_style)]
+   |            ^^^^^^^^^^^^^^^^^
+   = note: `#[warn(non_snake_case)]` implied by `#[warn(nonstandard_style)]`
+
+warning: 2 warnings emitted