Fix LimitStack::pop_atr in release builds (#16371)

in `LimitStack::pop_atr` always call `stack.pop()`.
It used to only be called inside a `debug_assert!` so the stack was not
popped in release builds.

Running `TESTNAME=cognitive_complexity cargo uitest --release` used to
print
```
error: there was 1 unmatched diagnostic
   --> tests/ui/cognitive_complexity.rs:121:4
    |
121 | fn bloo() {
    |    ^^^^ Error[clippy::cognitive_complexity]: the function has a cognitive complexity
 of (2/1)
    |
```

The first commit adds to the ui test, which also fails in release, the
2nd commit fixes the tests.

changelog: [`cognitive_complexity`]: fix attribute stack not popping in
release builds

clippy_utils/src/attrs.rs

@@ -159,7 +159,10 @@ impl LimitStack {
     }
     pub fn pop_attrs(&mut self, sess: &Session, attrs: &[impl AttributeExt], name: Symbol) {
         let stack = &mut self.stack;
-        parse_attrs(sess, attrs, name, |val| debug_assert_eq!(stack.pop(), Some(val)));
+        parse_attrs(sess, attrs, name, |val| {
+            let popped = stack.pop();
+            debug_assert_eq!(popped, Some(val));
+        });
     }
 }
 

tests/ui/cognitive_complexity.rs

@@ -472,3 +472,28 @@ mod issue14422 {
         return;
     }
 }
+
+#[clippy::cognitive_complexity = "1"]
+mod attribute_stacking {
+    fn bad() {
+        //~^ cognitive_complexity
+        if true {
+            println!("a");
+        }
+    }
+
+    #[clippy::cognitive_complexity = "2"]
+    fn ok() {
+        if true {
+            println!("a");
+        }
+    }
+
+    // should revert to cognitive_complexity = "1"
+    fn bad_again() {
+        //~^ cognitive_complexity
+        if true {
+            println!("a");
+        }
+    }
+}

tests/ui/cognitive_complexity.stderr

@@ -176,5 +176,21 @@ LL |     fn bar() {
    |
    = help: you could split it up into multiple smaller functions
 
-error: aborting due to 22 previous errors
+error: the function has a cognitive complexity of (2/1)
+  --> tests/ui/cognitive_complexity.rs:478:8
+   |
+LL |     fn bad() {
+   |        ^^^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: the function has a cognitive complexity of (2/1)
+  --> tests/ui/cognitive_complexity.rs:493:8
+   |
+LL |     fn bad_again() {
+   |        ^^^^^^^^^
+   |
+   = help: you could split it up into multiple smaller functions
+
+error: aborting due to 24 previous errors