Only comment out SET statements at the start of a line - #13

Description

The setup-postgres-preview-schema action rewrites the pg_dump output with sed before replaying it into the preview schema. The rule that comments out pg_dump's configuration statements was unanchored and global (s/SET /--SET /g), so it also rewrote every other occurrence of SET in the dump:

• ... ON DELETE SET NULL; → ... ON DELETE --SET NULL;
• ALTER COLUMN "c" SET DEFAULT ...; → ALTER COLUMN "c" --SET DEFAULT ...;

-- starts a SQL comment, so the rest of the statement is swallowed and the restore fails with a syntax error (observed in wm-connect-api, whose schema has an ON DELETE SET NULL foreign key: failing run).

How

Anchor the pattern to the start of the line: s/^SET /--SET /. pg_dump only emits its SET configuration statements (statement_timeout, search_path, ...) at column 0, while SET NULL / SET DEFAULT only occur mid-statement on indented lines, so the anchor cleanly separates the two. The g flag is dropped since only one SET can start a line.