fix(shorebird_cli): ensure system flutter pub get is run even if build fails

[bryanoltman]

Description

Wraps flutter build commands that use Shorebird's version of flutter in a try/finally that invokes flutter pub get in the finally block to ensure that .dart_tool/package_config.json points to the system version of Flutter whether or not the shorebird build succeeds.

Fixes #1193

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (db19456) 98.92% compared to head (d563728) 98.92%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1231   +/-   ##
=======================================
  Coverage   98.92%   98.92%           
=======================================
  Files         180      180           
  Lines        4574     4577    +3     
=======================================
+ Hits         4525     4528    +3     
  Misses         49       49           

Flag	Coverage Δ
shorebird_cli	100.00% <100.00%> (ø)

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Files Changed	Coverage Δ
...s/shorebird_cli/lib/src/shorebird_build_mixin.dart	100.00% <100.00%> (ø)

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[eseidel]

Very hard to read the diff, but assuming you're just wrapping in a finally, lgtm.