Treat escaped newline as valid sequence (#11465)

## Summary

We weren't treating the escaped newline as a valid condition to trigger
the safer fix (add an extra backslash before each invalid escape
sequence).

Closes https://github.com/astral-sh/ruff/issues/11461.

crates/ruff_linter/resources/test/fixtures/pycodestyle/W605_0.py

@@ -46,3 +46,15 @@ regex = '\\\_'
 
 #: W605:1:7
 u'foo\ bar'
+
+#: W605:1:13
+(
+    "foo \
+    bar \. baz"
+)
+
+#: W605:1:6
+"foo \. bar \t"
+
+#: W605:1:13
+"foo \t bar \."

crates/ruff_linter/src/rules/pycodestyle/rules/invalid_escape_sequence.rs

@@ -181,6 +181,7 @@ fn check(
 
         // If we're at the end of line, skip.
         if matches!(next_char, '\n' | '\r') {
+            contains_valid_escape_sequence = true;
             continue;
         }
 

crates/ruff_linter/src/rules/pycodestyle/snapshots/ruff_linter__rules__pycodestyle__tests__W605_W605_0.py.snap

@@ -145,6 +145,8 @@ W605_0.py:48:6: W605 [*] Invalid escape sequence: `\ `
 47 | #: W605:1:7
 48 | u'foo\ bar'
    |      ^^ W605
+49 | 
+50 | #: W605:1:13
    |
    = help: Use a raw string literal
 
@@ -154,5 +156,61 @@ W605_0.py:48:6: W605 [*] Invalid escape sequence: `\ `
 47 47 | #: W605:1:7
 48    |-u'foo\ bar'
    48 |+r'foo\ bar'
+49 49 | 
+50 50 | #: W605:1:13
+51 51 | (
 
+W605_0.py:53:9: W605 [*] Invalid escape sequence: `\.`
+   |
+51 | (
+52 |     "foo \
+53 |     bar \. baz"
+   |         ^^ W605
+54 | )
+   |
+   = help: Add backslash to escape sequence
 
+ℹ Safe fix
+50 50 | #: W605:1:13
+51 51 | (
+52 52 |     "foo \
+53    |-    bar \. baz"
+   53 |+    bar \\. baz"
+54 54 | )
+55 55 | 
+56 56 | #: W605:1:6
+
+W605_0.py:57:6: W605 [*] Invalid escape sequence: `\.`
+   |
+56 | #: W605:1:6
+57 | "foo \. bar \t"
+   |      ^^ W605
+58 | 
+59 | #: W605:1:13
+   |
+   = help: Add backslash to escape sequence
+
+ℹ Safe fix
+54 54 | )
+55 55 | 
+56 56 | #: W605:1:6
+57    |-"foo \. bar \t"
+   57 |+"foo \\. bar \t"
+58 58 | 
+59 59 | #: W605:1:13
+60 60 | "foo \t bar \."
+
+W605_0.py:60:13: W605 [*] Invalid escape sequence: `\.`
+   |
+59 | #: W605:1:13
+60 | "foo \t bar \."
+   |             ^^ W605
+   |
+   = help: Add backslash to escape sequence
+
+ℹ Safe fix
+57 57 | "foo \. bar \t"
+58 58 | 
+59 59 | #: W605:1:13
+60    |-"foo \t bar \."
+   60 |+"foo \t bar \\."