Bump third_party/base64 from `db7c683` to `387b32f` #1891

Job	Run time
build_macos (macos_release, Release, true, dmg)	12m 15s
build_linux (linux_release, Release, true, linuxes)	3m 24s
build_macos (macos_debug, Debug)	11m 47s
build_linux (linux_debug, Debug)	3m 11s
build_macos (macos_barebones, Debug, "BACKEND_JACK" = "Off", "HAVE_LV2" = "Off")	12m 25s
build_linux (linux_barebones, Release, "BACKEND_JACK" = "Off", "HAVE_LV2" = "Off")	3m 45s
build_linux (linux_asan, Debug, "ENABLE_ASAN" = "On")	3m 18s
build_windows (windows_release, windows-2022, python.exe, python.exe -m pip, windows, Release, tr...	9m 7s
build_linux (linux_coverage, Debug, "ENABLE_COVERAGE" = "On", true)	3m 24s
build_windows (windows_barebones, windows-2022, python.exe, python.exe -m pip, windows, Release, ...	6m 9s
build_windows (windows_debug, windows-2022, python.exe, python.exe -m pip, windows, Debug, 's/([^...	7m 2s
test_linux	0s
test_windows (release_windows, python.exe, python.exe -m pip, python.exe -m pytest, windows-2022,...	5m 38s
test_windows (release_windows_innosetup, python.exe, python.exe -m pip, python.exe -m pytest, win...	5m 52s
test_windows (debug_windows, python.exe, python.exe -m pip, python.exe -m pytest, windows-2022, w...	6m 8s
test_macos	0s
collect_crashes	25s
	1h 33m 50s

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