build-fail directive: make explanation more uniform
The last part of the paragraph did not fit
diff --git a/src/tests/ui.md b/src/tests/ui.md
index 09dc476..65bd89b 100644
--- a/src/tests/ui.md
+++ b/src/tests/ui.md
@@ -453,9 +453,9 @@
- `//@ check-fail` — compilation should fail (the codegen phase is skipped).
This is the default for UI tests.
- `//@ build-fail` — compilation should fail during the codegen phase.
- This will run `rustc` twice, once to verify that it compiles successfully
- without the codegen phase, then a second time the full compile should
- fail.
+ This will run `rustc` twice:
+ - First time is to ensure that the compile succeeds without the codegen phase
+ - Second time is to ensure that the full compile fails
- `//@ run-fail` — compilation should succeed, but running the resulting
binary should fail.
