[Infra] Disable Auth deprecations warnings in SPM CI (#14013)

Author: ncooke3

.github/workflows/spm.yml

@@ -21,6 +21,9 @@ concurrency:
     group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
     cancel-in-progress: true
 
+env:
+  FIREBASE_CI: true
+
 jobs:
   spm-package-resolved:
     env:

Package.swift

@@ -419,6 +419,7 @@ let package = Package(
         "ObjC", "Public",
       ],
       resources: [.process("Resources/PrivacyInfo.xcprivacy")],
+      swiftSettings: Context.environment["FIREBASE_CI"] != nil ? [.define("FIREBASE_CI")] : [],
       linkerSettings: [
         .linkedFramework("Security"),
         .linkedFramework("SafariServices", .when(platforms: [.iOS])),