fix: reduce memory usage in test

[shemau]

Description

Simplify the memory model used for basic testing. 4096 is the minimum size.
The multitenant other_test.go has been run and passed locally with the new lower memory.

Note: Error messages reporting 8192 (or more) are just multiplying the 4096 by the number of members.

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[shemau]

/run pipeline

[ocofaigh]

@shemau you happy to proceed?

[terraform-ibm-modules-ops]

🎉 This PR is included in version 3.19.4 🎉

The release is available on:

• GitHub release
• v3.19.4

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