.editorconfig

upgrade: fix handling of `.d` data file

The test did not used any `.d` file. So of course, their handling was broken
(for vfs encoding reason again). We fix the issue and update the test.

Note that  some fncache issue remains with `.d` file. It will be taken care of
in the next changesets.

Differential Revision: https://phab.mercurial-scm.org/D6904

# See http://EditorConfig.org for the specification

root = true

[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true

[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true

[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false