Prefer Regexp#match? over String#match?

This commit fixes a minor regression introduced in the commit e10a909

Prefer using `Regexp#match` because `@file` or `file` in these lines
could be `nil` if the `tag_markup` is just whitespace. In that scenario,
Jekyll should proceed to the validation logic and bail instead of raising
a `NoMethodError` exception.

History.markdown

@@ -164,7 +164,6 @@
   * Update TestTags in sync with Rouge v3.4 (#7709)
   * Bump RuboCop to v0.71.0 (#7687)
   * Use regexp to filter special entries (#7702)
-  * Replace `String#=~` with `String#match?` (#7718)
   * Reduce Array objects generated from utility method (#7749)
 
 ### Documentation

lib/jekyll/tags/include.rb

@@ -54,7 +54,7 @@ module Jekyll
       end
 
       def validate_file_name(file)
-        if file.match?(INVALID_SEQUENCES) || !file.match?(VALID_FILENAME_CHARS)
+        if INVALID_SEQUENCES.match?(file) || !VALID_FILENAME_CHARS.match?(file)
           raise ArgumentError, <<~MSG
             Invalid syntax for include tag. File contains invalid characters or sequences:
 
@@ -90,7 +90,7 @@ module Jekyll
 
       # Render the variable if required
       def render_variable(context)
-        Liquid::Template.parse(@file).render(context) if @file.match?(VARIABLE_SYNTAX)
+        Liquid::Template.parse(@file).render(context) if VARIABLE_SYNTAX.match?(@file)
       end
 
       def tag_includes_dirs(context)