ts:scripts: Use SOURCE_DATE_EPOCH env if available

See https://reproducible-builds.org/docs/source-date-epoch/

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

ts/scripts/get-expire-time.ts

@@ -8,7 +8,7 @@ import { writeFileSync } from 'fs';
 import { DAY } from '../util/durations';
 
 const unixTimestamp = parseInt(
-  execSync('git show -s --format=%ct').toString('utf8'),
+  process.env.SOURCE_DATE_EPOCH || execSync('git show -s --format=%ct').toString('utf8'),
   10
 );
 const buildCreation = unixTimestamp * 1000;