Allow to use higher versions of prometheus_client

Fixes matrix-org#7641

The package was pinned to <0.8.0 without an obvious reasoning with
7ad1d76
in matrix-org#5636
while the version selection looks to just try to exclude an arbitrary
next minor version number that might introduce API breaking changes.
Selecting the next minor number might be a good conservative selection.

Downstream distributions already reported success patching out the version
requirements.

This also fixes the integration of upgraded packages into openSUSE packages,
e.g. for openSUSE Tumbleweed which already ships prometheus_client >= 0.8 .

Signed-off-by: Oliver Kurz <okurz@suse.de>

changelog.d/7780.misc

@@ -0,0 +1 @@
+Allow to use higher versions of prometheus_client <0.9.0 which are expected to introduce no breaking changes. Contributed by Oliver Kurz.

synapse/python_dependencies.py

@@ -67,7 +67,7 @@
     "msgpack>=0.5.2",
     "phonenumbers>=8.2.0",
     "six>=1.10",
-    "prometheus_client>=0.0.18,<0.8.0",
+    "prometheus_client>=0.0.18,<0.9.0",
     # we use attr.s(slots), which arrived in 16.0.0
     # Twisted 18.7.0 requires attrs>=17.4.0
     "attrs>=17.4.0",