Annotate pattern bindings with refutable patterns

[fthomas]

This is in preparation for compiling with Scala 3 and prevents warnings about pattern bindings with refutable patterns like this:

 -- Warning: modules/core/src/test/scala/org/scalasteward/core/update/PruningAlgTest.scala:218:27
 218 |    val Right(repoCache) = decode[RepoCache](
     |                           ^
     |pattern's type Right[io.circe.Error, org.scalasteward.core.repocache.RepoCache] is more specialized than the right hand side expression's type Either[io.circe.Error, org.scalasteward.core.repocache.RepoCache]
     |
     |If the narrowing is intentional, this can be communicated by adding `: @unchecked` after the expression,
     |which may result in a MatchError at runtime.
     |This patch can be rewritten automatically under -rewrite -source 3.2-migration.

The changes here we done by the Scala 3 compiler by using the -rewrite -source 3.2-migration options. They are another large chunk of #2065 that have been cherry-picked from that branch.

Relevant documentation: https://docs.scala-lang.org/scala3/reference/changed-features/pattern-bindings.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.73%. Comparing base (040cef7) to head (1e1bad2).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3520   +/-   ##
=======================================
  Coverage   89.73%   89.73%           
=======================================
  Files         171      171           
  Lines        3536     3536           
  Branches      321      321           
=======================================
  Hits         3173     3173           
  Misses        363      363           

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