Fix master build case.
Fix master build case.

Otherwise, this will be built when building a specific
release tag (typically in the past), causing the master
binary to be overwritten with something older.

We can generally assume that tags will be applied after
the commit has been integrated, and therefore that any
builds pointing to tags will use only the tags.

Another way to fix this would be to introduce something
akin to the KOKORO_BUILD_NIGHTLY environment variable,
but it doesn't seem strictly necessary.

PiperOrigin-RevId: 291198171

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor