Coverity CI: add time to version

There has been just the date, add also the time and print date/time in
ISO 8601 in UTC.

Author: MartinPulec

.github/workflows/coverity-scan.yml

@@ -99,7 +99,7 @@ jobs:
         result=$(curl -Sf --form token=$coverity_token \
           --form email=pulec@cesnet.cz \
           --form file=@ultragrid.tar.xz \
-          --form version="$(date +%F)" \
+          --form version="$(date -u +%Y-%M-%dT%TZ)" \
           --form description="master build" \
           https://scan.coverity.com/builds?project=UltraGrid)
         echo "$result"