This includes a way to run two versions of the server from the TCL test
framework. It's a preparation to add more cross-version tests. The
runtest script accepts a new parameter
./runtest --other-server-path path/to/valkey-server
and a new tag "needs:other-server" for test cases and start_server.
Tests with this tag are automatically skipped if `--other-server-path`
is not provided.
This PR adds it in a CI job with Valkey 7.2.7 by downloading a binary
release.
Fixes#76
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Signed-off-by: Viktor Söderqvist <viktor.soderqvist@est.tech>
