Add mysql extension for sql scripts (#3413)

lib/linguist/languages.yml

@@ -3804,6 +3804,7 @@ SQL:
   - ".cql"
   - ".ddl"
   - ".inc"
+  - ".mysql"
   - ".prc"
   - ".tab"
   - ".udf"
@@ -4290,10 +4291,13 @@ Text:
   - COPYING
   - FONTLOG
   - INSTALL
+  - INSTALL.mysql
   - LICENSE
+  - LICENSE.mysql
   - NEWS
   - README.1ST
   - README.me
+  - README.mysql
   - click.me
   - delete.me
   - keep.me
@@ -4773,6 +4777,7 @@ YAML:
   - ".syntax"
   - ".yaml"
   - ".yaml-tmlanguage"
+  - ".yml.mysql"
   filenames:
   - ".clang-format"
   ace_mode: yaml