Fix expression language in the container when using the "container" variable
bug #12030 Fix expression language in the container when using the "container" variable (fabpot)

This PR was squashed before being merged into the 2.4 branch (closes #12030).

Discussion
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Fix expression language in the container when using the "container" variable

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11995
| License       | MIT
| Doc PR        | n/a

See #11995 for the description of the problem.

Commits
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2b2f0df Fix expression language in the container when using the "container" variable