Update the Xcode versions - 26.3 and 26.4b2 (swiftlang#245)

* Drop Xcode 26.0

Author: shahmishal

.github/workflows/swift_package_test.yml

@@ -9,7 +9,7 @@ on:
       macos_xcode_versions:
         type: string
         description: "Xcode version list (JSON)"
-        default: "[\"16.3\", \"16.4\", \"26.0\"]"
+        default: "[\"16.3\", \"16.4\", \"26.3\", \"26.4.b2\", ]"
       macos_exclude_xcode_versions:
         type: string
         description: "Exclude Xcode version list (JSON)"