fix dep in composer

Author: bshaffer

Spanner/composer.json

@@ -6,7 +6,7 @@
     "require": {
         "php": "^8.0",
         "ext-grpc": "*",
-        "google/cloud-core": "1.60",
+        "google/cloud-core": "^1.60",
         "google/gax": "dev-result-function as 1.40.0"
     },
     "require-dev": {