graph(ipfs-tests): task 4 — make GraphNodeConfig ipfs_uri configurable via env var

WARN (edge-case): Empty GRAPH_TEST_IPFS_URL values are not explicitly
checked (unlike test_utils.rs which guards against empty strings). The
requirement prescribes the unwrap_or_else pattern; an empty value would
produce an immediate connection error at graph-node startup, not silent
data corruption.

Note: 2 pre-existing test failures in gnd package
(test_schema_codegen_snapshot, test_format_typescript_graceful_fallback)
are outside this task's scope.

Author: isum

tests/src/config.rs

@@ -143,7 +143,8 @@ impl GraphNodeConfig {
         Self {
             bin,
             ports: GraphNodePorts::default(),
-            ipfs_uri: "http://localhost:3001".to_string(),
+            ipfs_uri: std::env::var("GRAPH_TEST_IPFS_URL")
+                .unwrap_or_else(|_| "http://127.0.0.1:3001".to_string()),
             log_file: TestFile::new("integration-tests/graph-node.log"),
         }
     }
@@ -157,7 +158,8 @@ impl Default for GraphNodeConfig {
         Self {
             bin,
             ports: GraphNodePorts::default(),
-            ipfs_uri: "http://localhost:3001".to_string(),
+            ipfs_uri: std::env::var("GRAPH_TEST_IPFS_URL")
+                .unwrap_or_else(|_| "http://127.0.0.1:3001".to_string()),
             log_file: TestFile::new("integration-tests/graph-node.log"),
         }
     }