[llvm] [gitattributes] Don't mark all llvm-rc test Inputs as binary (PR #68583)

[via llvm-commits]

serge-sans-paille wrote:

```sh
$ ls test/tools/llvm-rc/Inputs/ -1 | cut -d . -f 2 | sort -u
bmp
cur
html
ico
nested/
rc
```
This patch makes html and rc files visible, LGTM

https://github.com/llvm/llvm-project/pull/68583