Fix TraceurAppTests share sheet detection

When a user has not utilized the share sheet flow before "Share" will
appear instead of "Share with", potentially causing spurious failures.
Search for "Just once" instead to identify the share sheet.

Bug: 175764941
Test: presubmit
Change-Id: I2d27e06cebeeff1fa14d8d25b4caf9e947cbabfb
1 file changed