Update .gitattributes. (#24113)

Add .txt and remove the non-existent .py files.

.gitattributes

@@ -4,10 +4,10 @@
 *.js    text eol=lf
 *.json  text eol=lf
 *.md    text eol=lf
-*.py    text eol=lf
 *.rb    text eol=lf
 *.scss  text eol=lf
 *.svg   text eol=lf
+*.txt   text eol=lf
 *.yml   text eol=lf
 # Don't diff or textually merge source maps
 *.map   binary