Annotate out.test.toml with linguist-generated=true (#3617)

## Why
PRs like #3616 which change
out.test.toml cause massive diffs. Annotating these fields as generated
makes PRs easier to review.

## Tests
N/A

Author: shreyas-goenka

acceptance/.gitattributes

@@ -3,3 +3,6 @@
 # For example, an additional \r character in windows changes the upload payload if you are
 # uploading the file's content to a workspace.
 *.txt text eol=lf
+
+# The out.test.toml file is autogenerated based on the merged test.toml view.
+out.test.toml linguist-generated=true