Add PHP 7.4, fix Psalm issues

[Slamdunk]

Ping @paragonie-security

[lhchavez]

would you mind also adding

diff --git a/src/Parsing/PasetoMessage.php b/src/Parsing/PasetoMessage.php
index 8fe4839..132775d 100644
--- a/src/Parsing/PasetoMessage.php
+++ b/src/Parsing/PasetoMessage.php
@@ -47,7 +47,6 @@ final class PasetoMessage
      * @throws SecurityException
      * @throws InvalidVersionException
      * @throws InvalidPurposeException
-     * @return PasetoMessage
      * @throws \TypeError
      */
     public static function fromString(string $tainted): self

? That fixes another issue with the latest Psalm, since that function has a duplicate @return docstring tag.

[Slamdunk]

@lhchavez done, thank you

[Slamdunk]

ping @paragonie-scott @paragonie-security @paragonie-staff

[Slamdunk]

@paragonie-security as soon as this gets merged, I'll add a PR for PHP 8 compatibility

[stayallive]

I was looking to see if PHP 8 was on the radar, would be greatly appreciated if that is happening 👍