net.http: fix server_tls h2-negotiation test for default-on HTTP/2 (#27393)

test_server_tls_h2_negotiation asserted that a plain `http.fetch()` (no
`enable_http2` field) is served as HTTP/1.1. That held before #27384, but
#27384 flipped `enable_http2` to default `true`, so the client now advertises
`h2` ALPN by default and the server correctly upgrades — making the test's
`resp_h1.version() == .v1_1` assertion fail. This is currently red on master
CI (clang/gcc/tcc-linux, clang-macos).

The server behavior is correct; the test just needs to opt out explicitly.
Pass `enable_http2: false` on the HTTP/1.1 leg, which is what the test means
to exercise (server still serves h1 to a client that does not negotiate h2).

Co-authored-by: Richard Wheeler <quaesitor.scientiam@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: 3 people

vlib/net/http/server_tls_test.v

@@ -126,11 +126,13 @@ fn test_server_tls_h2_negotiation() {
 	assert resp.status_code == 200
 	assert resp.body == 'tls hello /h2'
 
-	// Without enable_http2 on the client, the server must keep speaking
-	// HTTP/1.1 to the same listener.
+	// With HTTP/2 disabled on the client, the server must keep speaking
+	// HTTP/1.1 to the same listener. (enable_http2 defaults to true since
+	// vlang/v#27384, so it must be opted out of explicitly here.)
 	resp_h1 := http.fetch(
-		url:      'https://127.0.0.1:${port}/h1'
-		validate: false
+		url:          'https://127.0.0.1:${port}/h1'
+		enable_http2: false
+		validate:     false
 	) or {
 		assert false, 'h1 fetch failed: ${err}'
 		return