sout: meson: fix protoc version check

Previous implementation was attempting to discard the micro version number in hopes that meson would ignore it while comparing protobuf and protoc versions. Unfortunately meson was trying to exact match the three components of the version anyway assuming the last one should be zero.

Extracted from the CI:

Run-time dependency protobuf found: YES 3.21.12
Running command: /usr/bin/protoc --version
--- stdout ---
libprotoc 3.21.12
--- stderr ---
Program protoc found: NO found 3.21.12 but need: '3.21' (/usr/bin/protoc)
modules/stream_out/chromecast/meson.build:21:38: ERROR: Tried to use not-found external program as generator

This patche fix the issue by introducing correct boundaries to the version check.