perf-test: rename time tests to have .sh suffix

This will simplify notmuch time tests

diff --git a/performance-test/T00-new b/performance-test/T00-new.sh
similarity index 100%
rename from performance-test/T00-new
rename to performance-test/T00-new.sh

diff --git a/performance-test/T01-dump-restore b/performance-test/T01-dump-restore.sh
similarity index 100%
rename from performance-test/T01-dump-restore
rename to performance-test/T01-dump-restore.sh

diff --git a/performance-test/T02-tag b/performance-test/T02-tag.sh
similarity index 100%
rename from performance-test/T02-tag
rename to performance-test/T02-tag.sh