Fix comment to match reality
We can't fix the code to match the comment, so have it the other way round.
diff --git a/library/certs.c b/library/certs.c
index 4ae3c24..7cc71ae 100644
--- a/library/certs.c
+++ b/library/certs.c
@@ -180,6 +180,10 @@
#if defined(MBEDTLS_SHA256_C)
/* tests/data_files/server2-sha256.crt */
+/* Or more precisely, this is the contents of the version of this file
+ * that's in the mbedtls-2.16 branch, due to a backporting mistake.
+ * We don't want to change the contents now, as that would change the size
+ * which is part of the ABI, which should be stable in LTS branches. */
#define TEST_SRV_CRT_RSA_SHA256 \
"-----BEGIN CERTIFICATE-----\r\n" \
"MIIDNzCCAh+gAwIBAgIBAjANBgkqhkiG9w0BAQsFADA7MQswCQYDVQQGEwJOTDER\r\n" \