ci: Add downstream project build testing (bp #13112) (#13119)

* Use local cargo for CI

(cherry picked from commit c7c50bd32c)

* Add downstream project build testing

(cherry picked from commit c7f4f15e60)

Co-authored-by: Michael Vines <mvines@gmail.com>

scripts/increment-cargo-version.sh

@@ -16,19 +16,7 @@ EOF
 here="$(dirname "$0")"
 cd "$here"/..
 source ci/semver_bash/semver.sh
-
-readCargoVariable() {
-  declare variable="$1"
-  declare Cargo_toml="$2"
-
-  while read -r name equals value _; do
-    if [[ $name = "$variable" && $equals = = ]]; then
-      echo "${value//\"/}"
-      return
-    fi
-  done < <(cat "$Cargo_toml")
-  echo "Unable to locate $variable in $Cargo_toml" 1>&2
-}
+source scripts/read-cargo-variable.sh
 
 ignores=(
   .cache