ci: run other loadtests to completion when one of them fails

The most likely offender to fail early is jwt-rsa-cache-worst - which
then cancels *all* loadtests at once. This is unnecessary churn for CI.
Instead we can re-run only that one test later.

.github/workflows/test.yaml

@@ -124,6 +124,7 @@ jobs:
 
   loadtest:
     strategy:
+      fail-fast: false
       matrix:
         kind: ['mixed', 'jwt-hs', 'jwt-hs-cache', 'jwt-hs-cache-worst', 'jwt-rsa', 'jwt-rsa-cache', 'jwt-rsa-cache-worst']
     name: Loadtest