pgsql: Constify the arguments of copydir.h functions

Constify the arguments of copydir.h functions

This makes sure that the internal logic of these functions does not
attempt to change the value of the arguments constified, and it removes
one unconstify() in basic_archive.c.

Author: Nathan Bossart
Reviewed-by: Andrew Dunstan, Peter Eisentraut
Discussion: https://postgr.es/m/20230114231126.GA2580330@nathanxps13

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2f31f405e1fa561db27e8dc6f7f3cb3dbd8c0c4f

Modified Files
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contrib/basic_archive/basic_archive.c | 2 +-
src/backend/storage/file/copydir.c    | 4 ++--
src/include/storage/copydir.h         | 4 ++--
3 files changed, 5 insertions(+), 5 deletions(-)