Fix a build error

This PR fixes the following build error.

```console
bundle exec rubocop
(snip)

Offenses:

lib/rubocop/cop/mixin/preceding_following_alignment.rb:96:9: W:
[Correctable] Lint/AmbiguousOperatorPrecedence: Wrap expressions with
varying precedence with parentheses to avoid ambiguity.
        range.source[-1] == '=' && line[range.last_column - 1] == '=' ||
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rubocop/cop/mixin/preceding_following_alignment.rb:101:9: W:
[Correctable] Lint/AmbiguousOperatorPrecedence: Wrap expressions with
varying precedence with parentheses to avoid ambiguity.
        range.source == '<<' && line[range.last_column - 1] == '=' ||
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rubocop/cop/mixin/preceding_following_alignment.rb:102:11: W:
[Correctable] Lint/AmbiguousOperatorPrecedence: Wrap expressions with
varying precedence with parentheses to avoid ambiguity.
          range.source[-1] == '=' && line[(range.last_column - 2)..(range.last_column - 1)] == '<<'
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rubocop/cop/mixin/preceding_following_alignment.rb:102:101:
C: Layout/LineLength: Line is too long. [101/100]
          (range.source[-1] == '=' && line[(range.last_column - 2)..(range.last_column - 1)] == '<<')
                                                                                                    ^

1304 files inspected, 4 offenses detected, 3 offenses corrected
```

https://github.com/rubocop/rubocop/runs/3453863216

lib/rubocop/cop/mixin/preceding_following_alignment.rb

@@ -93,13 +93,15 @@ def aligned_char?(range, line)
       end
 
       def aligned_assignment?(range, line)
-        range.source[-1] == '=' && line[range.last_column - 1] == '=' ||
+        (range.source[-1] == '=' && line[range.last_column - 1] == '=') ||
           aligned_with_append_operator?(range, line)
       end
 
       def aligned_with_append_operator?(range, line)
-        range.source == '<<' && line[range.last_column - 1] == '=' ||
-          range.source[-1] == '=' && line[(range.last_column - 2)..(range.last_column - 1)] == '<<'
+        last_column = range.last_column
+
+        (range.source == '<<' && line[last_column - 1] == '=') ||
+          (range.source[-1] == '=' && line[(last_column - 2)..(last_column - 1)] == '<<')
       end
 
       def aligned_identical?(range, line)