add .gitattribute to prevent line ending conversion on any machine

[cfbao]

Why

Git's line ending conversion has been tampering with our source code on GitHub Actions runners to be inequivalent to ones we use on our local machines.

Which line ending is used (LF vs CRLF) in raw string literals is determined by which one you use in the source file (well... they are "literals").
E.g. given the source code

string s = """
	1
	2
	""";
Console.WriteLine(s == "1\n2");
Console.WriteLine(s == "1\r\n2");

the program will

• print True False if the source file uses LF as newline characters
• print False True if the source file uses CRLF as newline characters

On our dev machines, we set core.autocrlf=false in Git and have end_of_line = lf in .editorconfig, so we always have LF as newline characters.
GitHub Actions Windows runners seems to be using core.autocrlf=true, so all source files were checked out with CRLF line endings...(!!!) and hence the executables built has different behaviour, because it doesn't use equivalent source code!

Unsetting the text attribute should disable line ending conversion entirely on any machine.

Ticket

https://desire2learn.atlassian.net/browse/VUL-447

[cfbao]

I think this is unfortunate naming on Git's part.
The text attribute only controls line ending conversion. It doesn't affect whether Git treats the file as text or binary.

See:
https://git-scm.com/docs/gitattributes#_text
https://stackoverflow.com/a/10017566/5916310