update-docs: accommodate for changes in Git v2.48.0

As of Git's 9219325be74 (Documentation: allow sourcing generated
includes from separate dir, 2024-12-06), there are no regular
`include::<path>` statements left that were expected by the
`update-docs.rb` script, but they are now `include::{build_dir}/<path>`
instead.

Let's accommodate for that.

This fixes git#1941

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

script/update-docs.rb

@@ -48,7 +48,7 @@ def wrap_front_matter(front_matter)
 end
 
 def expand_l10n(path, content, get_f_content, categories)
-  content.gsub!(/include::(\S+)\.txt/) do |line|
+  content.gsub!(/include::({build_dir}\/)?(\S+)\.txt/) do |line|
     line.gsub!("include::", "")
     if categories[line]
       new_content = categories[line]
@@ -240,7 +240,7 @@ def drop_uninteresting_tags(tags)
 end
 
 def expand_content(content, path, get_f_content, generated)
-  content.gsub(/include::(\S+)\.txt\[\]/) do |_line|
+  content.gsub(/include::(?:{build_dir}\/)?(\S+)\.txt\[\]/) do |_line|
     if File.dirname(path) == "."
       new_fname = "#{$1}.txt"
     else