When displaying multispans, ignore empty lines adjacent to `...`

```
error[E0308]: `match` arms have incompatible types
   --> tests/ui/codemap_tests/huge_multispan_highlight.rs:98:18
    |
6   |       let _ = match true {
    |               ---------- `match` arms have incompatible types
7   |           true => (
    |  _________________-
8   | |             // last line shown in multispan header
...   |
96  | |
97  | |         ),
    | |_________- this is found to be of type `()`
98  |           false => "
    |  __________________^
...   |
119 | |
120 | |         ",
    | |_________^ expected `()`, found `&str`

error[E0308]: `match` arms have incompatible types
   --> tests/ui/codemap_tests/huge_multispan_highlight.rs:215:18
    |
122 |       let _ = match true {
    |               ---------- `match` arms have incompatible types
123 |           true => (
    |  _________________-
124 | |
125 | |         1 // last line shown in multispan header
...   |
213 | |
214 | |         ),
    | |_________- this is found to be of type `{integer}`
215 |           false => "
    |  __________________^
216 | |
217 | |
218 | |         1 last line shown in multispan
...   |
237 | |
238 | |         ",
    | |_________^ expected integer, found `&str`
```

1 files changed, 0 insertions, 2 deletions

diff --git a/tests/rustdoc-ui/lints/check.stderr b/tests/rustdoc-ui/lints/check.stderr
index c5ed5d0c3ef..acdb8128443 100644
--- a/tests/rustdoc-ui/lints/check.stderr
+++ b/tests/rustdoc-ui/lints/check.stderr
@@ -4,7 +4,6 @@ warning: missing documentation for the crate
 LL | / #![feature(rustdoc_missing_doc_code_examples)]
 LL | |
 LL | |
-LL | |
 ...  |
 LL | |
 LL | | pub fn foo() {}
@@ -39,7 +38,6 @@ warning: missing code example in this documentation
 LL | / #![feature(rustdoc_missing_doc_code_examples)]
 LL | |
 LL | |
-LL | |
 ...  |
 LL | |
 LL | | pub fn foo() {}