bump: ubuntu version on CI

Signed-off-by: Thulio Ferraz Assis <3149049+f0rmiga@users.noreply.github.com>

.bazelci/presubmit.yml

diff --git a/.bazelci/presubmit.yml b/.bazelci/presubmit.yml
index e950d02..b7badf0 100644
--- a/.bazelci/presubmit.yml
+++ b/.bazelci/presubmit.yml
@@ -19,7 +19,7 @@
     # Disabled due to https://github.com/bazelbuild/rules_python/issues/827
     - "-//python/tests/toolchains:python_3_8_10_x86_64-apple-darwin_test"
 platforms:
-  ubuntu1804:
+  ubuntu2004:
     <<: *all_targets
   macos:
     <<: *all_targets