Standardizes JSON content type in test cases

Updates the `contentType` field in test cases to use "application/json"
instead of "application/json; charset=UTF-8" for consistency and to
align with expected content type format.

This change ensures uniformity in tests and avoids potential issues
related to charset specification.

Author: wilfredmulenga

server/internal/app/web_test.go

@@ -75,7 +75,7 @@ func TestWeb(t *testing.T) {
 			path:        "/reearth_config.json",
 			statusCode:  http.StatusOK,
 			body:        `{"a":"b","auth0Audience":"https://aud.example.com","auth0ClientId":"clientID","auth0Domain":"https://iss.example.com","published":"https://{}.example.com"}`,
-			contentType: "application/json; charset=UTF-8",
+			contentType: "application/json",
 		},
 		{
 			name:        "invalid path should serve index.html",
@@ -98,7 +98,7 @@ func TestWeb(t *testing.T) {
 			path:        "/data.json",
 			statusCode:  http.StatusNotFound,
 			body:        `{"error":"not found"}`,
-			contentType: "application/json; charset=UTF-8",
+			contentType: "application/json",
 		},
 		{
 			name:        "data file with host",