Reduce tab formatting assertions to debug only

The tab replacement for diagnostics added in #79757 included a few assertions to
ensure all tab characters are handled appropriately. We've started getting
reports of these assertions firing (#81614). Since it's only a cosmetic issue,
this downgrades the assertions to debug only, so we at least continue compiling
even if the diagnostics might be a tad wonky.

Fixes #81614

compiler/rustc_errors/src/styled_buffer.rs

@@ -15,7 +15,7 @@ impl StyledBuffer {
 
     pub fn render(&self) -> Vec<Vec<StyledString>> {
         // Tabs are assumed to have been replaced by spaces in calling code.
-        assert!(self.text.iter().all(|r| !r.contains(&'\t')));
+        debug_assert!(self.text.iter().all(|r| !r.contains(&'\t')));
 
         let mut output: Vec<Vec<StyledString>> = vec![];
         let mut styled_vec: Vec<StyledString> = vec![];