Fix math fork build problem by pinning to PR commit

[gnunicorn]

Fixes:

Changed 8 dependencies!
24 packages have newer versions incompatible with dependency constraints.
Try `flutter pub outdated` for more information.

Running Gradle task 'bundleRelease'...                          
/opt/hostedtoolcache/flutter/stable-3.16.0-x64/.pub-cache/hosted/pub.dev/flutter_math_fork-0.7.1/lib/src/widgets/selection/gesture_detector_builder_selectable.dart:38:22: Error: Type 'TapDragUpDetails' not found.
  void onSingleTapUp(TapDragUpDetails details) {
                     ^^^^^^^^^^^^^^^^
/opt/hostedtoolcache/flutter/stable-3.16.0-x64/.pub-cache/hosted/pub.dev/flutter_math_fork-0.7.1/lib/src/widgets/selection/gesture_detector_builder_selectable.dart:38:22: Error: 'TapDragUpDetails' isn't a type.
  void onSingleTapUp(TapDragUpDetails details) {
                     ^^^^^^^^^^^^^^^^
Target kernel_snapshot failed: Exception

By pinning the flutter_math_fork dependency to the fix from this PR

[Sese-Schneider]

@gnunicorn a fix version has been released on flutter_math_fork v0.7.2