Set SOURCE_DATE_EPOCH

[martincostello]

Set the SOURCE_DATE_EPOCH to the date of the checked-out Git commit to use for NuGet's DeterministicTimestamp in .NET 11.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.16%. Comparing base (9a4cb07) to head (2835272).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3115   +/-   ##
=======================================
  Coverage   96.16%   96.16%           
=======================================
  Files         311      311           
  Lines        7139     7139           
  Branches     1006     1006           
=======================================
  Hits         6865     6865           
  Misses        221      221           
  Partials       53       53           

Flag	Coverage Δ
linux	96.16% <ø> (ø)
macos	96.16% <ø> (ø)
windows	96.15% <ø> (ø)

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