fix(deps): update dependency matcher to ^0.12.20

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
matcher (source)	dependencies	patch	^0.12.16+1 → ^0.12.20

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Release Notes

dart-lang/test (matcher)

v0.12.20

Compare Source

• Allow exceptions from operator == to bubble up and fail the test instead of
  treating them as unequal objects.
• Require Dart 3.11

v0.12.19

Compare Source

• Improve speed of pretty printing for large collections.
• Improve output of pairwiseCompare with mismatched types.

v0.12.18

Compare Source

• Add isSorted and related matchers for iterables.
• Consider NaN to be equal to itself in equals.
• Remove some dynamic invocations.
• Add explicit casts from dynamic values.
• Require Dart 3.7

v0.12.17

Compare Source

• Require Dart 3.4
• Move to dart-lang/test monorepo.

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