tests/int: introduce the concept of unsafe tests

Some of runc integration tests may do something that I would not like
when running those on my development laptop. Examples include

 - changing the root mount propagation [1];
 - replacing /root/runc [2];
 - changing the file in /etc (see checkpoint.bats).

Yet it is totally fine to do all that in a throwaway CI environment,
or inside a Docker container.

Introduce a mechanism to skip specific "unsafe" tests unless an
environment variable, RUNC_ALLOW_UNSAFE_TESTS, is set. Use it
from a specific checkpoint/restore test which modifies
/etc/criu/default.conf.

[1]: https://github.com/opencontainers/runc/pull/5200
[2]: https://github.com/opencontainers/runc/pull/5207

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

.github/workflows/test.yml

@@ -18,6 +18,8 @@ env:
   LIBPATHRS_VERSION: "0.2.4"
   # Don't ignore C warnings. Note that the output of "go env CGO_CFLAGS" by default is "-g -O2", so we keep them.
   CGO_CFLAGS: -g -O2 -Werror
+  # Allow potentially unsafe tests.
+  RUNC_ALLOW_UNSAFE_TESTS: yes
 
 jobs:
   test: