Unfreeze firestore python generation

[sofisl]

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Summary of the issue

Firestore generation was skipped in #17413 because the firestore changes broke system tests.

Needs to be unskipped by removing this line:

google-cloud-python/librarian.yaml

Line 1154 in 2e75c78

skip_generate: true

API client name and version

No response

Reproduction steps: code

file: main.py

   def reproduce():
    # complete code here

Reproduction steps: supporting files

file: mydata.csv

alpha,1,3
beta,2,5

Reproduction steps: actual results

file: output.txtmydata.csv

Calculated: foo

Reproduction steps: expected results

file: output.txtmydata.csv

Calculated: bar

OS & version + platform

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Python environment

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Python dependencies

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Additional context

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