tests: Loosen error regexp

libcurl AFAICS doesn't have an API to convert HTTP code ➡️ error
string, so let's make the test regexp operate on both.

Closes: #651
Approved by: giuseppe

tests/test-pull-repeated.sh

@@ -34,7 +34,7 @@ for x in $(seq 200); do
 	echo "Success on iteration ${x}"
 	break;
     fi
-    assert_file_has_content err.txt "500.*Internal Server Error"
+    assert_file_has_content err.txt "\(500.*Internal Server Error\)\|\(HTTP 500\)"
 done
 
 ${CMD_PREFIX} ostree --repo=repo fsck

tests/test-pull-resume.sh

@@ -42,7 +42,7 @@ do
   if ${CMD_PREFIX} ostree --repo=repo pull origin main 2>err.log; then
     break
   fi
-  assert_file_has_content err.log 'error:.*Download incomplete'
+  assert_file_has_content err.log 'error:.*\(Download incomplete\)\|\(Transferred a partial file\)'
 done
 if ${CMD_PREFIX} ostree --repo=repo fsck; then
     echo "ok, pull succeeded!"