backport `gitlab-ci/lava: fix handling of lava tags` to 20.0

The lava tags was a python array not it's a gitlab CI string, slit the string with periods in the jinja2 template to avoid having the following tags :

tags:

• p
• a
• n
• f
• r
• o
• s
• t

instead of : tags:

• panfrost

Signed-off-by: Neil Armstrong narmstrong@baylibre.com Part-of: !4057 (merged) (cherry picked from commit bbdb4b1a)

Cc: @daenzer