Fix more shy group regexps

Fix more shy group regexps

These issues were caught by modified versions of the GNU ELPA
packages xr and relint:
- https://github.com/mattiase/xr/pull/6
- https://github.com/mattiase/relint/pull/14

* lisp/gnus/gnus-art.el (gnus-parse-news-url): Remove redundant
numbered group and calls to match-string.
* lisp/progmodes/c-ts-mode.el (c-ts-mode--c-or-c++-regexp): Fix shy
group mistyped as optional colon (bug#64019#29).
* lisp/vc/vc-git.el (vc-git-annotate-time): Ditto.  Also fix
timezone parsing by using iso8601-parse (bug#64069).
* test/lisp/vc/vc-git-tests.el (vc-git-test-annotate-time): New
test.