Mark all code blocks as C

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/docs/3.0-migration-guide.md b/docs/3.0-migration-guide.md
index c6e9c74..1b673f7 100644
--- a/docs/3.0-migration-guide.md
+++ b/docs/3.0-migration-guide.md
@@ -725,7 +725,7 @@
 ### SSL key export interface change
 
 This affects users of the SSL key export APIs:
-```
+```C
     mbedtls_ssl_conf_export_keys_cb()
     mbedtls_ssl_conf_export_keys_ext_cb()
 ```
@@ -876,7 +876,7 @@
 implementation to that of a key-value store with keys being
 session IDs and values being instances of `mbedtls_ssl_session`:
 
-```
+```C
 typedef int mbedtls_ssl_cache_get_t( void *data,
                                      unsigned char const *session_id,
                                      size_t session_id_len,
@@ -992,7 +992,7 @@
 The curve secp256k1 has also been removed from the default X.509 and TLS profiles. [RFC 8422](https://datatracker.ietf.org/doc/html/rfc8422#section-5.1.1) deprecates it in TLS, and it is very rarely used, although it is not known to be weak at the time of writing.
 
 If you still need to accept certificates signed with algorithms that have been removed from the default profile, call `mbedtls_x509_crt_verify_with_profile` instead of `mbedtls_x509_crt_verify` and pass a profile that allows the curves and hashes you want. For example, to allow SHA-224:
-```
+```C
 mbedtls_x509_crt_profile my_profile = mbedtls_x509_crt_profile_default;
 my_profile.allowed_mds |= MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA224 );
 ```