dylan update should skip certain directories

[cgay]

In particular, _test, _build, and _packages should be ignored.

17:52:55 ~/dylan/workspaces/dylan-tool (dev*) 
$ dylan-tool-app update
Downloaded pacman-catalog@master to /home/cgay/.local/state/dylan/_packages/pacman-catalog/master/src/
Downloaded strings@1.1.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/strings/1.1.0/src/
Downloaded command-line-parser@3.1.1 to /home/cgay/dylan/workspaces/dylan-tool/_packages/command-line-parser/3.1.1/src/
Downloaded uncommon-dylan@0.2.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/uncommon-dylan/0.2.0/src/
Downloaded json@1.0.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/json/1.0.0/src/
Downloaded logging@2.1.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/logging/2.1.0/src/
Downloaded sphinx-extensions@0.2.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/sphinx-extensions/0.2.0/src/
Downloaded testworks@2.0.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/testworks/2.0.0/src/
Downloaded regular-expressions@0.2.0 to /home/cgay/dylan/workspaces/dylan-tool/_packages/regular-expressions/0.2.0/src/
WARNING: LID file /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175015/test-parse-lid-file--lid-header/child.lid has no (transitive) 'Files' property.
WARNING: LID file /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175015/test-parse-lid-file--lid-header/parent.lid has no (transitive) 'Files' property.
WARNING: LID file /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175146/test-parse-lid-file--lid-header/child.lid has no (transitive) 'Files' property.
WARNING: LID file /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175146/test-parse-lid-file--lid-header/parent.lid has no (transitive) 'Files' property.
WARNING: Library "abc" has multiple .lid files for platform "x86_64-linux".
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175146/test-source-file-map--included-lid/abc.lid
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175015/test-source-file-map--included-lid/abc.lid
Registry will point to the first one, arbitrarily.
WARNING: Library "foo" has multiple .lid files for platform "x86_64-linux".
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175146/test-parse-lid-file--lid-header/parent.lid
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175146/test-source-file-map--basics/foo.lid
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175015/test-parse-lid-file--lid-header/parent.lid
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175015/test-source-file-map--basics/foo.lid
Registry will point to the first one, arbitrarily.
WARNING: Library "abc-test-suite" has multiple .lid files for platform "x86_64-linux".
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175146/test-source-file-map--included-lid/abc-test-suite.lid
  /home/cgay/dylan/workspaces/dylan-tool/_test/cgay-20230528-175015/test-source-file-map--included-lid/abc-test-suite.lid
Registry will point to the first one, arbitrarily.
Updated 27 files in /home/cgay/dylan/workspaces/dylan-tool/registry/.