Fix behavior with pg_restore -l and compressed dumps

pg_restore -l has always been able to read the TOC data of a dump even
if its binary has no support for compression, for both compressed and
uncompressed dumps.  5e73a60 has introduced a backward-incompatible
behavior by switching a warning to a hard error in the code path reading
the header data of a dump, preventing the TOC items to be listed even if
pg_restore -l, with no support for compression, is used on a compressed
dump.  Most modern systems should have support for zlib, but it can be
also possible that somebody relies on the past behavior when copying
over a dump where binaries are not built with zlib support (most likely
some WIN32 flavors these days, though most environments should provide
that).

There is no easy way to have a regression test for this pattern, as it
requires a mix of dump/restore commands with different compilation
options, with and without compression.  One possibility I see here would
be to have a command-line option that enforces a non-compression check
for a build that supports compression, but that does not seem worth the
cost, either.

Reported-by: Justin Pryzby
Author: Georgios Kokolatos
Discussion: https://postgr.es/m/20230125180020.GF22427@telsasoft.com

src/bin/pg_dump/pg_backup_archiver.c

@@ -3784,7 +3784,7 @@ ReadHead(ArchiveHandle *AH)
 
 #ifndef HAVE_LIBZ
 	if (AH->compression_spec.algorithm == PG_COMPRESSION_GZIP)
-		pg_fatal("archive is compressed, but this installation does not support compression");
+		pg_log_warning("archive is compressed, but this installation does not support compression -- no data will be available");
 #endif
 
 	if (AH->version >= K_VERS_1_4)