Fix Data.findFirstTypeMismatch to check all elements of Bundles (backport #3928)

[mergify]

This is an automatic backport of pull request #3928 done by Mergify.

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Original PR Body

Fix embarrassing bug introduced in #3201. Basically, DataMirror.checkTypeEquivalence is only checking the first element of Bundles 🙈

Fixes #3922

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
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• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Bugfix

Desired Merge Strategy

• Squash

Release Notes

Fixes DataMirror.checkTypeEquivalence to actually check all fields of Bundles and Records. This may expose latent bugs in user code.

Reviewer Checklist (only modified by reviewer)

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• Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
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