Use git-commit language for hub pull-request files

Whereas `git commit` uses a file called `COMMIT_EDITMSG`, the hub[^1]
command-line tool uses a file called `PULLREQ_EDITMSG`[^2]. This file is
used to edit the message of each commit being submitted in a pull
request, so it makes sense to reuse the git-commit language.

This commit adds `PULLREQ_EDITMSG` to the list of git-commit file-types.

[^1]: https://github.com/github/hub
[^2]: https://github.com/github/hub/blob/c8e68d548a39ec0fab6f674a669c21b54d4eec61/commands/pull_request.go#L225

languages.toml

@@ -1086,7 +1086,7 @@ source = { git = "https://github.com/camdencheek/tree-sitter-dockerfile", rev =
 name = "git-commit"
 scope = "git.commitmsg"
 roots = []
-file-types = ["COMMIT_EDITMSG"]
+file-types = ["COMMIT_EDITMSG", "PULLREQ_EDITMSG"]
 comment-token = "#"
 indent = { tab-width = 2, unit = "  " }
 rulers = [50, 72]