Mark internal messages as no longer translatable

The problem that these messages protect against can only occur because
a corrupted hash spill file was written, i.e., a Postgres bug.  There's
no reason to have them as translatable.

Backpatch to 15, where these messages were changed by commit c4649cce39.

Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/20230510175407.dwa5v477pw62ikyx@alvherre.pgsql

src/backend/executor/nodeAgg.c

@@ -3022,7 +3022,7 @@ hashagg_batch_read(HashAggBatch *batch, uint32 *hashp)
 	if (nread != sizeof(uint32))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("unexpected EOF for tape %p: requested %zu bytes, read %zu bytes",
+				 errmsg_internal("unexpected EOF for tape %p: requested %zu bytes, read %zu bytes",
 								 tape, sizeof(uint32), nread)));
 	if (hashp != NULL)
 		*hashp = hash;
@@ -3031,7 +3031,7 @@ hashagg_batch_read(HashAggBatch *batch, uint32 *hashp)
 	if (nread != sizeof(uint32))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("unexpected EOF for tape %p: requested %zu bytes, read %zu bytes",
+				 errmsg_internal("unexpected EOF for tape %p: requested %zu bytes, read %zu bytes",
 								 tape, sizeof(uint32), nread)));
 
 	tuple = (MinimalTuple) palloc(t_len);
@@ -3043,7 +3043,7 @@ hashagg_batch_read(HashAggBatch *batch, uint32 *hashp)
 	if (nread != t_len - sizeof(uint32))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("unexpected EOF for tape %p: requested %zu bytes, read %zu bytes",
+				 errmsg_internal("unexpected EOF for tape %p: requested %zu bytes, read %zu bytes",
 								 tape, t_len - sizeof(uint32), nread)));
 
 	return tuple;