docs(readme): bump action version to v5 - #130

The base and head of this comparison were measured with different runner settings, so their benchmark values are not directly comparable.

What changed between base and head:

• CodSpeed runner v5.0.0 changed how benchmarks are measured (base 4.18.3 → head 5.0.0). View release notes
• Cycle estimation (off → on) changes how benchmark performance is calculated. Learn more about cycle estimation
• Allocator-time exclusion (off → on) removes allocator time from the measurement, which shifts benchmark values. Learn more about allocator-time exclusion
• CodSpeed runner v5.0.0 changed how benchmarks are measured (base 4.18.1 → head 5.0.0). View release notes

Re-run the base with the same settings to get a valid performance comparison.

_{Comparing cod-3244-bump-action-v5 (64cbb82) with master (65832cc)}