Fix GPG temp path too long issue for FOSS build

Detailed discussion can be found on github (https://github.com/bazelbuild/bazel/issues/3215). On newer Debian systems as well as on macOS, the temporary folder created to store gpg configs are too long, which results in an error:

gpg: can't connect to the agent: File name too long

This CL makes affected tests use /tmp as temp folder base. Other options are discussed in the github issue, but this one seems to be the mostly non-harmful one. Note that this change only affect the FOSS build, as internal builds are not affected by the temp directory issue, probably due to the internal build tool using a different base temp directory.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=178803914

javatests/google/registry/rde/BUILD

@@ -50,6 +50,10 @@ java_library(
 GenTestRules(
     name = "GeneratedTestRules",
     default_test_size = "large",
+    # TODO (b/63619837): stop using hardcoded /tmp once
+    # https://github.com/bazelbuild/bazel/issues/3215 is resolved.
+    # If /tmp is not accessible, try changing it to one that is.
+    jvm_flags = ["-Djava.io.tmpdir=/tmp"],
     test_files = glob(
         ["*Test.java"],
         exclude = ["RdeUploadActionTest.java"],