Upgrade requests-cache as current version breaks CI pipelines

Due to some changes very high up the stack in CPython 3.9.10 [1],
requests-cache does no longer work properly [2] and will fail due to
its dependency on cattrs [3] which uses functools.singledispatch
which is what changed in the aforementioned CPython update.

The requests-cache devs have implemented a workaround in version
0.9.1 which is the only thing that they can do since cattrs does
not explicitly support their usage (and are not willing to
implement a workaround at their level).

This commit upgrades to said version.

[1] https://bugs.python.org/issue46032
[2] requests-cache/requests-cache#504
[3] python-attrs/cattrs#206

requirements.txt

@@ -583,9 +583,9 @@ requests==2.26.0 \
     #   requests-kerberos
     #   requests-oauthlib
     #   requests-toolbelt
-requests-cache==0.8.1 \
-    --hash=sha256:27d3eb276ab3affa9864dfc0475241d6d960dd566d57ec46ffa7759c2c74ed1c \
-    --hash=sha256:f36104f95ee78bba3d13a2692fe7c0fa8623872275949836789d98d359e79390
+requests-cache==0.9.1 \
+    --hash=sha256:3e3384c48dca231ee4c49e7ba53162bc0d99e16721baf085bfba1552d065d151 \
+    --hash=sha256:7737f83f0f48481a904bb9a9402233db5090931e46f9644c502646a573848d35
     # via -r requirements.in
 requests-gssapi==1.2.3 \
     --hash=sha256:20784508981401f7153c933eed095338933a40818da65a259dbf2d80dccb150e