swift-snapshot-testing needs upgrade for 6.1

Author: tayloraswift

Scripts/Linux/GeneratePackageSymbolGraphs

@@ -23,7 +23,7 @@ ssgc slave https://github.com/swiftlang/swift-syntax.git 600.0.1 \
     -u $SWIFT_INSTALLATION \
     -o TestPackages/swift-syntax.bson
 
-ssgc slave https://github.com/pointfreeco/swift-snapshot-testing.git 1.17.5 \
+ssgc slave https://github.com/pointfreeco/swift-snapshot-testing.git 1.18.3 \
     -u $SWIFT_INSTALLATION \
     -o TestPackages/swift-snapshot-testing.bson