chore: copy and update PROPERTIES using widely supported syntax (#1779)

Author: burkedavison

rules_java_gapic/java_gapic_pkg.bzl

@@ -25,7 +25,8 @@ def _wrapPropertyNamesInBraces(properties):
 # the version of protobuf defined in googleapis is higher than protobuf
 # defined in gax-java/dependencies.properties, use this replacement to
 # sync the two versions.
-SYNCED_PROPERTIES = PROPERTIES | {"version.com_google_protobuf": PROTOBUF_JAVA_VERSION}
+SYNCED_PROPERTIES = dict(PROPERTIES)
+SYNCED_PROPERTIES.update({"version.com_google_protobuf": PROTOBUF_JAVA_VERSION})
 _PROPERTIES = _wrapPropertyNamesInBraces(SYNCED_PROPERTIES)
 
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