Fix 3865 - Disable scriptencoding vint error. (#3866)

- Add .vintrc.yaml configuration that disables the scriptencoding check
  (ProhibitMissingScriptEncoding) that is raised randomly.
- Upgrade vint to 0.3.21. Project seems to have stopped here and 0.4.0
  was never released.
- Ensure the run-test scripts use the correct docker image (e.g. add tag)
  .

Co-authored-by: Horacio Sanson <horacio@allm.inc>

.vintrc.yaml

@@ -0,0 +1,5 @@
+policies:
+  # Disable a violation that is thrown randomly for reasons I still
+  # do not understand.
+  ProhibitMissingScriptEncoding:
+    enabled: false