buildbucket: fix buildername regexp to include () chars.
buildbucket: fix buildername regexp to include () chars.

R=smut

Bug: 1082187
Change-Id: Ic47f2a00a56c555745dc9aedfec19f5ee3c0f405
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2200282
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: smut <95deb7aa15d4c615299e47e7688551456568b1fb@google.com>
Auto-Submit: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Reviewed-by: smut <95deb7aa15d4c615299e47e7688551456568b1fb@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go