Add ui test for incorrect type of ensure argument

tests/ui/ensure-nonbool.rs

@@ -0,0 +1,13 @@
+use anyhow::{ensure, Result};
+
+fn main() -> Result<()> {
+    ensure!("...");
+
+    struct Struct(bool);
+    let mut s = Struct(true);
+    match &mut s {
+        Struct(cond) => ensure!(cond),
+    }
+
+    Ok(())
+}

tests/ui/ensure-nonbool.stderr

@@ -0,0 +1,15 @@
+error[E0600]: cannot apply unary operator `!` to type `&'static str`
+ --> tests/ui/ensure-nonbool.rs:4:5
+  |
+4 |     ensure!("...");
+  |     ^^^^^^^^^^^^^^ cannot apply unary operator `!`
+  |
+  = note: this error originates in the macro `$crate::__fallback_ensure` which comes from the expansion of the macro `ensure` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0600]: cannot apply unary operator `!` to type `&mut bool`
+ --> tests/ui/ensure-nonbool.rs:9:25
+  |
+9 |         Struct(cond) => ensure!(cond),
+  |                         ^^^^^^^^^^^^^ cannot apply unary operator `!`
+  |
+  = note: this error originates in the macro `$crate::__fallback_ensure` which comes from the expansion of the macro `ensure` (in Nightly builds, run with -Z macro-backtrace for more info)