Add items to license allowlist.

Add the following items to the allowlsted licenses based on the
requirement of crrev.com/c/6239492 :
 - PngSuite
 - Spencer-86
 - unicode_org

Bug: 378472917
Change-Id: I6dfa79d612131eae154e5030ec22b787ebc57060
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6243133
Commit-Queue: Jordan Brown <rop@google.com>
Auto-Submit: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Jordan Brown <rop@google.com>

metadata/fields/custom/license_allowlist.py

@@ -95,6 +95,7 @@ ALLOWED_SPDX_LICENSES = frozenset([
     "OpenSSL",
     "Python-2.0",
     "SGI-B-2.0",
+    "Spencer-86",
     "SunPro",
     "Unicode-3.0",
     "Unicode-DFS-2015",
@@ -147,8 +148,10 @@ EXTENDED_LICENSE_CLASSIFIERS = frozenset([
     "LicenseRef-OpenGLUT",
     "LicenseRef-takuya-ooura",
     "pffft",
+    "PngSuite",
     "Punycode",
     "SSLeay",
+    "unicode_org",
     "WebM-Project-Patent",
     "X11-Lucent",
     "zxing",
@@ -201,4 +204,4 @@ WITH_PERMISSION_ONLY = frozenset([
 
 ALLOWED_LICENSES = ALLOWED_SPDX_LICENSES | EXTENDED_LICENSE_CLASSIFIERS
 ALLOWED_OPEN_SOURCE_LICENSES = ALLOWED_LICENSES | OPEN_SOURCE_SPDX_LICENSES
-ALL_LICENSES = ALLOWED_OPEN_SOURCE_LICENSES | WITH_PERMISSION_ONLY
+ALL_LICENSES = ALLOWED_OPEN_SOURCE_LICENSES | WITH_PERMISSION_ONLY