Fix DRBG_internal alloc in wc_RNG_HealthTestLocal

[embhorn]

Description

Fix allocation of DRBG_internal to 1 element of DRBG_internal

Fixes #9846

Testing

Confirmed visually

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[Copilot]

Pull request overview

Fixes an incorrect allocation size for DRBG_internal in wc_RNG_HealthTestLocal by allocating a single DRBG_internal element instead of treating sizeof(DRBG_internal) as an element count.

Changes:

• Update WC_ALLOC_VAR_EX usage to allocate 1 element of DRBG_internal (instead of sizeof(DRBG_internal) elements).

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[embhorn]

Jenkins retest this please

Build [wolfSSL » PRB-140-3-tests #8676](https://cloud.wolfssl-test.com/jenkins/job/wolfSSL/job/PRB-140-3-tests/8676/) completed: SUCCESS
[Pipeline] }
ERROR: No build record wolfSSL/PRB-140-3-tests#8676 could be located.
Setting overall build result to FAILURE