Add openSUSE Tumbleweed/Leap support (#1166)

<!---
❗️ Please read ❗️
➡️ Please make sure you've followed the guidelines:
https://github.com/angristan/openvpn-install#contributing
✅ Please make sure your changes are tested and working
🗣️ Please avoid large PRs, and discuss changes in a GitHub issue first
✋ If the changes are too big and not in line with the project, they will
probably be rejected. Remember that this script is meant to be simple
and easy to use.
--->

---------

Co-authored-by: Stanislas Lange <git@slange.me>

Makefile

@@ -111,6 +111,12 @@ test-arch:
 test-centos-stream-9:
 	$(MAKE) test BASE_IMAGE=quay.io/centos/centos:stream9
 
+test-opensuse-leap:
+	$(MAKE) test BASE_IMAGE=opensuse/leap:16.0
+
+test-opensuse-tumbleweed:
+	$(MAKE) test BASE_IMAGE=opensuse/tumbleweed
+
 # Test all distributions (runs sequentially)
 test-all:
 	$(MAKE) test-ubuntu-18.04
@@ -130,3 +136,5 @@ test-all:
 	$(MAKE) test-amazon-2023
 	$(MAKE) test-arch
 	$(MAKE) test-centos-stream-9
+	$(MAKE) test-opensuse-leap
+	$(MAKE) test-opensuse-tumbleweed