Fix incompatible Rails cache version from 7.1 to 6.1

What does this MR do and why?

GitLab 18.0 is using Rails cache format version of 7.1 which is not backwards compatible to previous cache format version 6.1 (GitLab 17.11 and before)

The application could break (does not load) on some scenarios where:

• Instance upgraded to 18.0+, but later downgraded to 17.11
• Local development environment changed from master to an older branch, pre 18.0 release.
• Zero-downtime upgrade is performed from 17.11 to -> 18.0.x.

The fix is to treat the new format as a cache miss.

References

Exception request issue: https://gitlab.com/gitlab-org/release/tasks/-/issues/20141

#552652 (closed)

!195052 (comment 2578440325)

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