Fix typographical errors

[Pronoss]

This PR addresses typographical errors in comments and test descriptions within the following files:

Files Changed:

1. File: ChildTransaction.ts

   • Corrected "an child chain transaction" to "a child chain transaction."

2. File: childBlocksForL1Block.test.ts

   • Corrected "an Child block range" to "a Child block range" in multiple test descriptions.

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