Make bug report issue template more similar to that of rust-lang/rust (#16047)

It's always a bit jarring to be required to provide the expected output
first, as usually one starts with having the existing output, and
modifies that.

This commit reorders the two steps, and also gives them the same names
as `rust-lang/rust` for some extra consistency

changelog: none

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -20,15 +20,15 @@ body:
       label: Reproducer
       description: Please provide the code and steps to reproduce the bug
       value: |
-        I tried this code:
+        Code:
 
         ```rust
         <code>
         ```
 
-        I expected to see this happen:
+        Current output:
 
-        Instead, this happened:
+        Desired output:
   - type: textarea
     id: version
     attributes: