Make unit tests work on ubuntu 24.04 (#48151)

`kcov` was removed in Ubuntu 24.04, and it is no longer
installable via `apt` in our CI images. Instal it via
Linuxbrew instead, at least until it comes back to Ubuntu.

`subversion` is also not installed on ubuntu 24 by default,
so we have to install it manually.

- [x] Add linuxbrew to linux tests
- [x] Install `kcov` with brew
- [x] Install subversion with `apt`

Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>

share/spack/qa/run-shell-tests

@@ -36,7 +36,7 @@ export QA_DIR=$(realpath $QA_DIR)
 cd "$SPACK_ROOT"
 
 # Run bash tests with coverage enabled, but pipe output to /dev/null
-# because it seems that kcov seems to undo the script's redirection
+# because it seems that kcov undoes the script's redirection
 if [ "$COVERAGE" = true ]; then
     kcov "$SPACK_ROOT/coverage" "$QA_DIR/setup-env-test.sh" &> /dev/null
     kcov "$SPACK_ROOT/coverage" "$QA_DIR/completion-test.sh" &> /dev/null