1.0.8

Fix JSON parsing errors in Mattermost notification workflows

Replace manual sed-based JSON escaping with jq for proper handling of
special characters in PR/issue descriptions. This fixes the 'Expected
comma or closing brace' JSON parsing errors that occurred when
descriptions contained backticks, backslashes, or other special chars.

Changes:
- pullrequest-mattermost.yaml: Use jq with --arg for JSON construction
- issues-mattermost.yaml: Use jq for both issue and comment bodies
- builds-mattermost.yaml: Remove toJSON() wrapper, simplify with jq

All workflows now properly escape quotes, backslashes, newlines, and
other JSON-sensitive characters in notification payloads.