Run 'make update-copyright'.
* lib/regexprops.c (copying): Update the year number manually.
The format of the copyright year number range in Texinfo files is
"YEAR1--YEAR2" now, i.e., with 2x '-'.
* tests/sample-test: Likewise, here to avoid starting a year number range.
* All other files: Update copyright years via the above make run.
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