Some OpenAPI calls inherit invalid Host header when needing to `getChangeFeed()`.

What did you do?

1. Start a cluster

   tiup playground-ng v8.5.8 --db 1 --kv 1 --pd 1 --ticdc 1 --tiflash 0 --without-monitor --ticdc.config ./ticdc-newarch.toml
   

2. Create an empty changefeed

   tiup cdc:v8.5.8 cli changefeed  create -c test --sink-uri 'blackhole://'
   

3. List the changefeeds using OpenAPI v2 with an invalid Host header

   curl -H 'Host: example.invalid' http://127.0.0.1:8300/api/v2/changefeeds
   

4. List tables in the test changefeed using OpenAPI v2 with an invalid Host header

   curl -H 'Host: example.invalid' http://127.0.0.1:8300/api/v2/changefeeds/test/tables
   

What did you expect to see?

Either both 3 and 4 are invalid, or both 3 and 4 work fine.

What did you see instead?

Step 3 returned valid result, while step 4 returned HTTP 500.

{
    "error_msg": "Get \"http://example.invalid/api/v2/changefeeds/test?keyspace=default\": dial tcp: lookup example.invalid: no such host",
    "error_code": ""
}

Versions of the cluster

v8.5.8

Reproduce the discrepancy with the TiUP cluster and the two curl commands in the issue. Then trace the OpenAPI v2 handlers for /api/v2/changefeeds and /api/v2/changefeeds/{id}/tables, focusing on getChangeFeed and Host handling; done means both requests behave consistently with an invalid Host header and the regression is covered by an appropriate test.