Psalm-issues batch #4 (#1166)

lib/SimpleSAML/HTTP/RunnableResponse.php

lib/SimpleSAML/XHTML/Template.php

psalm.xml

tests/BuiltInServer.php

tests/SigningTestCase.php

tests/Utils/ReduceSpillOverTest.php

tests/lib/SimpleSAML/DatabaseTest.php

tests/lib/SimpleSAML/Metadata/SAMLBuilderTest.php

tests/lib/SimpleSAML/Metadata/SAMLParserTest.php

...eSAML/Metadata/test-metadata/source1/saml20-sp-remote.php

tests/lib/SimpleSAML/SessionHandlerPHPTest.php

tests/lib/SimpleSAML/Store/RedisTest.php

tests/lib/SimpleSAML/Store/SQLTest.php

tests/lib/SimpleSAML/StoreTest.php

tests/lib/SimpleSAML/Utils/ArraysTest.php

tests/lib/SimpleSAML/Utils/AttributesTest.php

tests/lib/SimpleSAML/Utils/Config/MetadataTest.php

tests/lib/SimpleSAML/Utils/CryptoTest.php

tests/lib/SimpleSAML/Utils/HTTPTest.php

tests/lib/SimpleSAML/Utils/SystemTest.php