Add .swig and .swg extension to SWIG (#7480)

* languages: add .swg and .swig as SWIG extensions

* SWIG: add .swig and .swg samples

code from https://github.com/google/or-tools/tree/main

Author: Mizux

lib/linguist/languages.yml

@@ -6814,6 +6814,8 @@ SWIG:
   type: programming
   extensions:
   - ".i"
+  - ".swg"
+  - ".swig"
   tm_scope: source.c++
   ace_mode: c_cpp
   codemirror_mode: clike