Trivial: update git attributes for Makefile (#638)

* Update .gitattributes for Go files

- Mark go source files as text, with LF line ending.
- Set git diff language mode for `*.go` files to `golang`

* Add .gitattributes entry for Makefiles

.gitattributes

@@ -1,2 +1,4 @@
-*.go	whitespace=trailing-space,space-before-tab,indent-with-non-tab
-go.mod	whitespace=trailing-space,space-before-tab,indent-with-non-tab
+*.go	text eol=lf whitespace=trailing-space,space-before-tab,indent-with-non-tab diff=golang
+go.mod	text eol=lf whitespace=trailing-space,space-before-tab,indent-with-non-tab
+go.sum	text eol=lf whitespace=trailing-space,space-before-tab,indent-with-non-tab
+Makefile text eol=lf whitespace=trailing-space,space-before-tab,indent-with-non-tab