Add Swift 5.6. (#3516)

Adds Swift 5.6 as a compiler option.

etc/config/swift.amazon.properties

@@ -1,9 +1,9 @@
 compilers=&swift
-demangler=/opt/compiler-explorer/swift-5.5/usr/bin/swift-demangle
-defaultCompiler=swift55
+demangler=/opt/compiler-explorer/swift-5.6/usr/bin/swift-demangle
+defaultCompiler=swift56
 objdumper=/opt/compiler-explorer/gcc-snapshot/bin/objdump
 
-group.swift.compilers=swift311:swift402:swift403:swift41:swift411:swift412:swift42:swift50:swift51:swift52:swift53:swift54:swift55:swiftnightly
+group.swift.compilers=swift311:swift402:swift403:swift41:swift411:swift412:swift42:swift50:swift51:swift52:swift53:swift54:swift55:swift56:swiftnightly
 group.swift.isSemVer=true
 group.swift.baseName=x86-64 swiftc
 compiler.swift311.exe=/opt/compiler-explorer/swift-3.1.1/usr/bin/swiftc
@@ -40,6 +40,8 @@ compiler.swift54.exe=/opt/compiler-explorer/swift-5.4/usr/bin/swiftc
 compiler.swift54.semver=5.4
 compiler.swift55.exe=/opt/compiler-explorer/swift-5.5/usr/bin/swiftc
 compiler.swift55.semver=5.5
+compiler.swift56.exe=/opt/compiler-explorer/swift-5.6/usr/bin/swiftc
+compiler.swift56.semver=5.6
 compiler.swiftnightly.exe=/opt/compiler-explorer/swift-nightly/usr/bin/swiftc
 compiler.swiftnightly.semver=nightly