Fix execution concurrency level for single-core systems

[zi0Black]

Description

Small check for emulated environments where we can have a single CPU core.
@JoshLind if you prefer a one line we can update this.

How Has This Been Tested?

N/A

Key Areas to Review

N/A

Type of Change

• New feature
• Bug fix
• Breaking change
• Performance improvement
• Refactoring
• Dependency update
• Documentation update
• Tests

Which Components or Systems Does This Change Impact?

• Validator Node
• Full Node (API, Indexer, etc.)
• Move/Aptos Virtual Machine
• Aptos Framework
• Aptos CLI/SDK
• Developer Infrastructure
• Move Compiler
• Other (specify)

Checklist

• I have read and followed the CONTRIBUTING doc
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I identified and added all stakeholders and component owners affected by this change as reviewers
• I tested both happy and unhappy path of the functionality
• I have made corresponding changes to the documentation

[trunk-io]

⏱️ 21m total CI duration on this PR

Job	Cumulative Duration	Recent Runs
check-dynamic-deps	10m	🟩 🟩 🟩 🟩
rust-cargo-deny	7m	🟩 🟩 🟩 🟩
general-lints	2m	🟩 🟩 🟩 🟩
semgrep/ci	2m	🟩 🟩 🟩 🟩
file_change_determinator	48s	🟩 🟩 🟩 🟩
permission-check	8s	🟩 🟩 🟩 🟩
permission-check	7s	🟩 🟩 🟩 🟩

_{settings ⋅ feedback ⋅ docs ⋅ learn more about trunk.io}

[graphite-app]

The range 0..=MAX_RETRIES is inclusive and will result in 4 attempts (0,1,2,3). To match the intended MAX_RETRIES value of 3, consider using 0..MAX_RETRIES instead, which will perform exactly 3 attempts.

Spotted by Graphite Reviewer

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