py-httpie: update to 2.6.0.

# 2.6.0

- Added support for formatting & coloring of JSON bodies preceded by non-JSON data (e.g., an XXSI prefix).
- Added charset auto-detection when `Content-Type` doesn窶冲 include it.
- Added `--response-charset` to allow overriding the response encoding for terminal display purposes.
- Added `--response-mime` to allow overriding the response mime type for coloring and formatting for the terminal.
- Added the ability to silence warnings through using `-q` or `--quiet` twice (e.g. `-qq`)
- Added installed plugin list to `--debug` output.
- Fixed duplicate keys preservation in JSON data.

# 2.5.0

Blog post: [What窶冱 new in HTTPie 2.5.0](https://httpie.io/blog/httpie-2.5.0)

- Added `--raw` to allow specifying the raw request body without extra processing as
  an alternative to `stdin`.
- Added support for XML formatting.
- Added internal support for file-like object responses to improve adapter plugin support.
- Fixed `--continue --download` with a single byte to be downloaded left.
- Fixed `--verbose` HTTP 307 redirects with streamed request body.
- Fixed handling of session files with `Cookie:` followed by other headers.

(wiz)