Fix: Resolve code gen in Flutter version 3.27.1

[haitr]

Problem
It fails to start due to incompatibility issues with updated versions of the analyzer and source_span packages.

Solution
Pin the versions of analyzer and source_span packages.

Changes
Updated pubspec.yaml to fix package versions:

• analyzer: pinned to version 6.9.0
• source_span: pinned to version 1.8.0

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[haitr]

@cla-bot check

[cla-bot]

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[victorcode1]

This needs to be resolved

[nirinchev]

I think this can only be merged as a short-term fix - pinning the analyzer package like that can cause incompatibilities with other generators that may require different versions.

As far as I understand, the failure reported in #1813 is due to element3 being added to DartType - could we instead of pinning the analyzer, provide a noSuchMethod implementation that returns never? Or does this break in a different way?