chore: update link to async api specification

[IgorKarpiuk]

What/Why/How?

Replace old link to async api specification v2.6.0

Reference

Testing

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Check yourself

• Code is linted
• Tested with redoc/reference-docs/workflows (internal)
• All new/updated code is covered with tests

Security

• Security impact of change has been considered
• Code follows company security practices and guidelines

[changeset-bot]

⚠️ No Changeset found

Latest commit: 38a5a10

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

Command	Mean [s]	Min [s]	Max [s]	Relative
redocly lint packages/core/src/benchmark/benches/rebilly.yaml	1.025 ± 0.028	0.984	1.078	1.00
redocly-next lint packages/core/src/benchmark/benches/rebilly.yaml	1.032 ± 0.020	1.002	1.065	1.01 ± 0.03

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	76.19%	4073/5346
🟡	Branches	66.07%	2169/3283
🟡	Functions	68.43%	661/966
🟡	Lines	76.38%	3820/5001

Test suite run success

652 tests passing in 94 suites.

Report generated by 🧪jest coverage report action from 38a5a10