CI: Use branch-versioned cargo throughout (#13411)

(cherry picked from commit 66c3c6c2b3)

Co-authored-by: Trent Nelson <trent@solana.com>

install/install-help.sh

@@ -2,8 +2,9 @@
 set -e
 
 cd "$(dirname "$0")"/..
+cargo="$(readlink -f "./cargo")"
 
-cargo build --package solana-install
+"$cargo" build --package solana-install
 export PATH=$PWD/target/debug:$PATH
 
 echo "\`\`\`manpage"