tools: fixup issue with building env

Missed to append in last CL one extra flag in start_venv.sh

BUG=b:449664590
TEST=built venv on Cloudtop
     as in readme instructions - able to use tools

Change-Id: I091e1804fef5c421a791c74d686a9aeaafda88bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dolos/+/7016009
Tested-by: Łukasz Hajec <[email protected]>
Commit-Queue: Michał Headcrab Barnaś <[email protected]>
Auto-Submit: Łukasz Hajec <[email protected]>
Reviewed-by: Michał Headcrab Barnaś <[email protected]>
1 file changed