ENH: Update double-conversion import script to record prior import

In commit ee51ee1 (ENH: Update Double-convert third-party,
2020-12-26, v5.2rc01~19) the double-conversion code was updated
directly in our tree instead of merging an upstream vendor branch.
Record the version whose content was imported.

Modules/ThirdParty/DoubleConversion/UpdateDoubleConversionFromGoogle.sh

@@ -8,7 +8,7 @@ readonly name="DoubleConversion"
 readonly ownership="Google double-conversion Maintainers <floitsch@google.com>"
 readonly subtree="Modules/ThirdParty/DoubleConversion/src/double-conversion"
 readonly repo="https://github.com/google/double-conversion"
-readonly tag="master"
+readonly tag="0d3733a4168dd739f45cef8a55718f8b02ee3073"
 readonly paths="
 double-conversion/*.h
 double-conversion/*.cc