fix: openid-connect plugin - existing session randomly unavailable for introspection / token renewal

[brentmjohnson]

Description

Fixes #9306

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• (NA - should be handled by existing tests) I have added tests corresponding to this change
• (NA - no change to interfaces) I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[shreemaan-abhishek]

can you add test cases for this?

[shreemaan-abhishek]

@brentmjohnson we are waiting for your response.

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