fix: adds html content type to index.html (#3845)

Author: amir20

internal/web/__snapshots__/web.snapshot

@@ -2,15 +2,15 @@
 HTTP/1.1 200 OK
 Connection: close
 Content-Security-Policy: default-src 'self' 'wasm-unsafe-eval' blob: https://cdn.jsdelivr.net https://*.duckdb.org; style-src 'self' 'unsafe-inline' blob:; img-src 'self' data:;
-Content-Type: text/plain; charset=utf-8
+Content-Type: text/html; charset=utf-8
 
 foo page
 
 /* snapshot: Test_createRoutes_index */
 HTTP/1.1 200 OK
 Connection: close
 Content-Security-Policy: default-src 'self' 'wasm-unsafe-eval' blob: https://cdn.jsdelivr.net https://*.duckdb.org; style-src 'self' 'unsafe-inline' blob:; img-src 'self' data:;
-Content-Type: text/plain; charset=utf-8
+Content-Type: text/html; charset=utf-8
 
 index page
 
@@ -87,7 +87,6 @@ Content-Type: text/html
 /* snapshot: Test_handler_between_dates_with_everything_complex */
 {"m":{"msg":"a complex log message"},"ts":1589396197772,"id":62280847,"l":"unknown","s":"stdout","c":"123456"}
 
-
 /* snapshot: Test_handler_between_dates_with_fill */
 {"m":"INFO Testing stdout logs...","ts":1589396137772,"id":466600245,"l":"info","s":"stdout","c":"123456"}
 {"m":"INFO Testing stderr logs...","ts":1589396197772,"id":1101501603,"l":"info","s":"stderr","c":"123456"}

internal/web/index.go

@@ -103,6 +103,7 @@ func (h *handler) executeTemplate(w http.ResponseWriter, req *http.Request) {
 		log.Fatal().Err(err).Msg("Could not parse index.html")
 	}
 
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	err = tmpl.Execute(w, data)
 	if err != nil {
 		log.Fatal().Err(err).Msg("Could not execute index.html")