ci/b2c: add support for the new format of CI_RUNNER_TAGS

Seems like Gitlab did not follow their own documentation:

```
CI_RUNNER_TAGS  8.10  0.5  A comma-separated list of the runner tags.
```

But it would seem like a gitlab update brought json-style lists which
broke:

```
CI_RUNNER_TAGS = '["keywords-gateway", "CI-gateway"]'
```

This commit adds support for both style.

Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>
Reviewed-by: John Brooks <john@fastquake.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18923>

.gitlab-ci/b2c/generate_b2c.py

@@ -24,6 +24,7 @@
 from jinja2 import Environment, FileSystemLoader
 from argparse import ArgumentParser
 from os import environ, path
+import json
 
 
 parser = ArgumentParser()
@@ -69,7 +70,10 @@ values['log_level'] = args.log_level
 values['poweroff_delay'] = args.poweroff_delay
 values['session_end_regex'] = args.session_end_regex
 values['session_reboot_regex'] = args.session_reboot_regex
-values['tags'] = args.tags
+try:
+    values['tags'] = json.loads(args.tags)
+except json.decoder.JSONDecodeError:
+    values['tags'] = args.tags.split(",")
 values['template'] = args.template
 values['timeout_boot_minutes'] = args.timeout_boot_minutes
 values['timeout_boot_retries'] = args.timeout_boot_retries