Fix incorrect usage of gp_versionstr in pg_upgrade version check

Previously, the Cloudberry-specific version string was incorrectly written
into `versionstr` instead of `gp_versionstr`, breaking the fallback comparison
logic in `check_exec()`. This caused version checks to fail when the program
output matched the expected Apache Cloudberry format.

Author: yjhjstz

src/backend/access/rmgrdesc/nbtdesc.c

@@ -26,7 +26,7 @@ out_insert(StringInfo buf, uint8 info, XLogReaderState *record)
 	char		*ptr;
 	xl_btree_insert	*xlrec = (xl_btree_insert *) rec;
 	xl_btree_metadata *md;
-	BlockNumber	blkno;	
+	BlockNumber	blkno = InvalidBlockNumber;
 	bool		fullpage;
 	Size		datalen;
 

src/bin/pg_upgrade/exec.c

@@ -457,7 +457,7 @@ check_exec(const char *dir, const char *program, bool check_version)
 		pg_strip_crlf(line);
 
 		snprintf(versionstr, sizeof(versionstr), "%s (PostgreSQL) " PG_VERSION, program);
-		snprintf(versionstr, sizeof(versionstr), "%s (Apache Cloudberry) " PG_VERSION, program);
+		snprintf(gp_versionstr, sizeof(versionstr), "%s (Apache Cloudberry) " PG_VERSION, program);
 
 		if (strcmp(line, versionstr) != 0 && strcmp(line, gp_versionstr) != 0)
 			pg_fatal("check for \"%s\" failed: incorrect version: found \"%s\", expected \"%s\" or \"%s\"\n",