remove testground #15

Job	Run time
workspace-check / workspace-check	14m 15s
core-cargo-test / core-cargo-test (windows-latest, x86_64-pc-windows-msvc)	24m 41s
core-cargo-test / core-cargo-test (ubuntu-latest, x86_64-unknown-linux-gnu)	13m 17s
core-cargo-test / core-cargo-test (macos-latest, x86_64-apple-darwin)	17m 12s
core-build-and-draft / core-build-and-draft (windows-latest, x86_64-pc-windows-msvc, windows, x86_64, .exe, false)	32m 1s
core-build-and-draft / core-build-and-draft (ubuntu-latest, x86_64-unknown-linux-gnu, linux, x86_64, false)	18m 20s
core-build-and-draft / core-build-and-draft (self-hosted, aarch64-unknown-linux-gnu, linux, aarch64, false)	3m 59s
core-build-and-draft / core-build-and-draft (macos-latest, x86_64-apple-darwin, macos, x86_64, false)	26m 1s
dashboard-build-and-draft / dashboard-build-and-draft (windows-latest, x86_64-pc-windows-msvc)	20m 33s
dashboard-build-and-draft / dashboard-build-and-draft (ubuntu-latest, x86_64-unknown-linux-gnu)	35m 48s
dashboard-build-and-draft / dashboard-build-and-draft (macos-latest, x86_64-apple-darwin)	18m 21s
	3h 44m 28s

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