chore: update install.sh prerelease version to v0.7.0-rc8

Signed-off-by: Jan Pokorný <JenomPokorny@gmail.com>

Author: JanPokorny

install.sh

@@ -6,7 +6,7 @@ set -eu
 
 # These get updated by `mise release`:
 LATEST_STABLE_AGENTSTACK_VERSION=0.6.2
-LATEST_AGENTSTACK_VERSION=0.7.0-rc7
+LATEST_AGENTSTACK_VERSION=0.7.0-rc8
 
 # This gets updated by Renovate:
 # renovate: datasource=python-version depName=python