Pin Spring Boot 2.x for GCP auth extension testing

Author: trask

.github/renovate.json5

@@ -87,6 +87,17 @@
       "matchPackagePrefixes": ["jakarta.servlet:"],
       "matchCurrentVersion": "5.0.0",
       "enabled": false
+    },
+    {
+      // intentionally using Spring Boot 2 in gcp-auth-extension in order to test with Java 8+
+      "matchFileNames": [
+        "gcp-auth-extension/build.gradle.kts"
+      ],
+      "matchPackageNames": [
+        "org.springframework.boot:org.springframework.boot.gradle.plugin", // this is for plugin id "org.springframework.boot"
+        "org.springframework.boot:spring-boot-dependencies"],
+      "matchUpdateTypes": ["major", "minor"],
+      "enabled": false,
     }
   ]
 }