[CI] Hook cli-tests up to CI

Add cli-tests to `make test`. This adds a `python3` dependency to `make
test`, but not `make check`. We could make this dependency optional by
skipping the tests if `python3` is not present.

tests/cli-tests/common/format.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-source "$COMMON/platform.sh"
+. "$COMMON/platform.sh"
 
 zstd_supports_format()
 {

tests/cli-tests/common/mtime.sh

@@ -1,4 +1,4 @@
-source "$COMMON/platform.sh"
+. "$COMMON/platform.sh"
 
 MTIME="stat -c %Y"
 case "$UNAME" in

tests/cli-tests/common/permissions.sh

@@ -1,4 +1,4 @@
-source "$COMMON/platform.sh"
+. "$COMMON/platform.sh"
 
 GET_PERMS="stat -c %a"
 case "$UNAME" in