docs: add missing default stamp var

[alexeagle]

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Changes are visible to end-users: no

Test plan

none

[aspect-workflows]

Test

4 test targets passed

Targets

//docs:update_24_test [k8-fastbuild]                         60ms
//lib/tests/copy_to_directory_bin_action:test [k8-fastbuild] 173ms
//lib/tests/jq:check_stamped [k8-fastbuild]                  304ms
//lib/tests/yq:check_stamped [k8-fastbuild]                  440ms

Total test execution time was 977ms. 213 tests (98.2%) were fully cached saving 43s.

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Test

e2e/copy_action

All tests were cache hits

1 test (100.0%) was fully cached saving 73ms.

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Test

e2e/copy_to_directory

All tests were cache hits

6 tests (100.0%) were fully cached saving 583ms.

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Test

e2e/coreutils

All tests were cache hits

4 tests (100.0%) were fully cached saving 423ms.

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Test

e2e/external_copy_to_directory

All tests were cache hits

1 test (100.0%) was fully cached saving 73ms.

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Test

e2e/smoke

All tests were cache hits

6 tests (100.0%) were fully cached saving 2s.

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Buildifier      Format      Gazelle