Allow template tests to have trailing empty lines

[mamachanko]

This makes it easier to author template tests, because editors tend to append a newline when saving files.

Previously, ERR: template test could not have trailing empty lines. I am using both Vim and IntelliJ. Both make it hard to remove the last line break in the file. I spend a minute to figure it out, and in Vim you can do :set noendofline binary for a buffer and it trims trailing whitespace. But that's a bother.

I think it is better testing UX this way. I held back from letting my IDE add a line break to existing *.tpltest.

[mamachanko]

@pivotaljohn thank you so much for taking action and addressing the linter-flagged issues! The failing PR checks were overlooked by me. 🙇🏻

Furthermore, I forgot to mention that test/filetests/filetests_test.go tests both for spaces and tabs, but GitHub doesn't display whitespace characters sufficiently different (which is what one wants most of the time), e.g.

├──┤├──┤├──┤give:·`␊
we␊
␊
··want├──┤␊
├──┤yaml␊
␊
`,␊
├──┤├──┤├──┤want:·`␊
we␊
␊
··want␊
├──┤yaml`,␊

[pivotaljohn]

With this, you've eliminated one of the last (the last?) vestiges of pain around writing these kinds of tests. That's important because this style of testing ought to be the workhorse for this codebase.

🙏🏻