Experiment for empty xref-index on CI + Racket 6.12 #1397

Job	Run time
Windows Emacs 29.1 and Racket stable	7m 19s
Windows Emacs 29.1 and Racket stable	7m 19s
Ubuntu Emacs 25.1 and Racket 6.12	4m 37s
Ubuntu Emacs 25.1 and Racket 6.12	4m 37s
Ubuntu Emacs 25.1 and Racket stable	5m 1s
Ubuntu Emacs 25.1 and Racket stable	5m 1s
Ubuntu Emacs 26.3 and Racket 6.12	4m 4s
Ubuntu Emacs 26.3 and Racket 6.12	4m 42s
Ubuntu Emacs 26.3 and Racket stable	4m 28s
Ubuntu Emacs 26.3 and Racket stable	4m 28s
Ubuntu Emacs 29.1 and Racket 6.12	4m 39s
Ubuntu Emacs 29.1 and Racket 6.12	4m 39s
Ubuntu Emacs 29.1 and Racket stable	4m 47s
Ubuntu Emacs 29.1 and Racket stable	4m 47s
Ubuntu Emacs snapshot and Racket current	4m 32s
Ubuntu Emacs snapshot and Racket current	4m 32s
	1h 19m 32s

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