Add support for reportlab 3.6 to the dev_requirements.txt

AFAICT the system worked just fine with this before, but the
requirements.txt specifically locked in the version thats in Debian
Bullseye.

Generally it's still recommended to use the packaged version (which
worked with both Bullseye and Bookworm already).

Fixes #122 (even though nothing actually changes)

tools/devsetup/dev_requirements.txt

@@ -10,7 +10,7 @@ flup
 httplib2
 psycopg2-binary
 pycryptodomex==3.6.1
-reportlab==3.5.59
+reportlab>=3.5.59,<3.7
 python-dateutil
 requests
 requests-oauthlib==1.0.0