fix: bump sqlc fork to v1.31.1 merge, strip pg_dump meta-commands (#25105)

Closes https://github.com/coder/internal/issues/965

Recent `pg_dump` patch releases (13.22+ / 14.19+ / 15.14+ / 16.10+ /
17.6+) emit `\restrict` / `\unrestrict` psql meta-commands at the head
and tail of schema dumps. These broke both `sqlc` and our
`scripts/migrate-test` schema-equality check. PR #19696 worked around it
by pinning `pg_dump` to a Docker image.

This change unpins the workaround now that `sqlc` handles the
meta-commands:

* Bumps the coder/sqlc fork pin to [`337309b` on
coder/sqlc:main](https://github.com/coder/sqlc/commit/337309bfb9524f38466a5090e310040fc7af0203),
the merge of upstream v1.31.1 (coder/sqlc#6). v1.31.1 includes
[sqlc-dev/sqlc#4390](https://github.com/sqlc-dev/sqlc/pull/4390), the
upstream `\restrict` / `\unrestrict` parser fix. Updated in three places
that pin the fork SHA: `flake.nix` (`sqlc-custom`),
`.github/actions/setup-sqlc/action.yaml`, and the
`dogfood/coder/ubuntu-{22,26}.04` Dockerfiles. The flake's `sha256` /
`vendorHash` are reset to `pkgs.lib.fakeSha256`; Nix will surface the
real hashes on first build, per the existing comment block.
* Reverts #19696's Docker pin in `coderd/database/dbtestutil/db.go`.
Local `pg_dump` (13+) and the `postgres:13` Docker fallback both work
again.
* Strips `\restrict` / `\unrestrict` lines in `normalizeDump` so
`scripts/migrate-test`'s schema comparison is stable across `pg_dump`
versions (the token in those lines is randomized per run).
`TestNormalizeDumpStripsRestrict` locks the behavior in.
* Regenerates with v1.31.1, picking up the version stamp and one
upstream correctness fix in `DeleteLicense`
([sqlc-dev/sqlc#4383](https://github.com/sqlc-dev/sqlc/pull/4383): don't
shadow the input parameter when scanning a single-column return).

coderd/database/queries.sql.go

@@ -1,6 +1,6 @@
 // Code generated by sqlc. DO NOT EDIT.
 // versions:
-//   sqlc v1.30.0
+//   sqlc v1.31.1
 
 package database
 
@@ -12997,8 +12997,9 @@ RETURNING id
 
 func (q *sqlQuerier) DeleteLicense(ctx context.Context, id int32) (int32, error) {
 	row := q.db.QueryRowContext(ctx, deleteLicense, id)
-	err := row.Scan(&id)
-	return id, err
+	var id_2 int32
+	err := row.Scan(&id_2)
+	return id_2, err
 }
 
 const getLicenseByID = `-- name: GetLicenseByID :one