Potential fix for code scanning alert no. 173: Incomplete string escaping or encoding

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: p-linnane

Formula/p/php@8.1.rb

@@ -91,7 +91,7 @@ def install
 
       # apxs will interpolate the @ in the versioned prefix: https://bz.apache.org/bugzilla/show_bug.cgi?id=61944
       s.gsub! "LIBEXECDIR='$APXS_LIBEXECDIR'",
-              "LIBEXECDIR='" + "#{lib}/httpd/modules".gsub("@", "\\@") + "'"
+              "LIBEXECDIR='" + "#{lib}/httpd/modules".gsub("\\", "\\\\\\\\").gsub("@", "\\@") + "'"
     end
 
     # Update error message in apache sapi to better explain the requirements