Minor: reduce indent level in page filter pruning code

[alamb]

Which issue does this PR close?

Part of #5104

Rationale for this change

I am working to fix the page pruning logic to handle schemas that are not the same across files. I find the nesting level of the page pruning code hard to work and I want to minimize the diff of the PR that will make actual logic changes to make it easier to review.

What changes are included in this PR?

1. Reduces the nesting level.

No functional changes are intended

Are these changes tested?

Covered by existing tests

Are there any user-facing changes?

No

[alamb]

Reviewing with whitespace blind diff I think shows more easily what is changed https://github.com/apache/arrow-datafusion/pull/5105/files?w=1

[alamb]

@Ted-Jiang or @tustvold or @thinkharderdev I wonder if you might have time over the next few days to review this (mechanical) PR (in support of trying to get page index enabled by default)?

[ursabot]

Benchmark runs are scheduled for baseline = f8607c2 and contender = 8bae10b. 8bae10b is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java