runtime(yaml): update YAML indentation for mapping keys inside list items

runtime(yaml): update YAML indentation for mapping keys inside list items

When a list item contains a mapping key (e.g., '- element1:'), the
content under that key was incorrectly indented. The indent function
was not accounting for the '- ' prefix when calculating indentation
for nested content.

Example that now works correctly:
  list:
    - element1:
        foo: bar  # Now correctly at indent 6, not 4

The fix adds special handling in two places:
1. When previous line ends with ':' and starts with '- '
2. When looking up previous mapping key that is a list item

Fixes indentation to account for the 2-character '- ' prefix.

fixes:  #18943
closes: #19133

Signed-off-by: Cezar Dimoiu <cezar.dimoiu@keysight.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>