🐛 MutationObserver bug fix for privacy level

[jagracey]

Motivation

Noticed a bug on an internal session replay where a text node was treated with the wrong privacy level.
The text node was masked by default instead of allowed- which turns out to be a good fail safe for "private by default"👍.

Changes

Testing

Adds a new test to catch in the future.

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I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

Merging #1038 (540a6dd) into main (c24c0ff) will decrease coverage by 0.01%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main    #1038      +/-   ##
==========================================
- Coverage   88.95%   88.93%   -0.02%     
==========================================
  Files          88       88              
  Lines        4163     4166       +3     
  Branches      957      958       +1     
==========================================
+ Hits         3703     3705       +2     
- Misses        460      461       +1     

Impacted Files	Coverage Δ
packages/rum/src/domain/record/mutationObserver.ts	95.65% <75.00%> (-0.65%)	⬇️

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