diagnostics, ui: Adjust to 'read-error' and 'syntax-error' in Guile 3.0.6.

diagnostics, ui: Adjust to 'read-error' and 'syntax-error' in Guile 3.0.6.

* guix/diagnostics.scm (source-properties->location): Add clause for
vectors.
* guix/ui.scm (report-load-error): Tweak 'read-error' handling for 3.0.6.
* tests/guix-package.sh: Relax regexp for the "unbound variable"
diagnostic check.
* tests/guix-system.sh: Adjust "missing closing paren" check for 3.0.6.
* tests/records.scm (location-alist): New procedure.
("define-record-type* & wrong field specifier")
("define-record-type* & wrong field specifier, identifier")
("define-record-type* & duplicate initializers"): Use it.