Lock filelock to version 3.4.0 to retain python 2.7 support

Filelock was upgraded to 3.4.2 from 3.4.0 over the holidays,
and this breaks our build that requires python 2.7 compatibility.
We'll stay with 3.4.0 which has worked for StarlingX for some time,
rather than reverting to 3.2.1 which was the last with official
python 2.7 support.

Closes-Bug: 1956054
Signed-off-by: Scott Little <scott.little@windriver.com>
Change-Id: I77e595f7fcf081707da78f2fba8df70bf19033de

toCOPY/builder-constraints.txt

@@ -1,2 +1,3 @@
 more-itertools===5.0.0;python_version=='2.7' # Last version with official 2.7 support
-pyparsing===2.4.7;python_version=='2.7'
+pyparsing===2.4.7
+filelock===3.4.0  # Last version with official support was 3.2.1, but 3.4.0 is known to work