ci: use uv to install gcovr and sphinx

Change-Id: If41dc0b522c70f462b62c34f54c40f73c39565b1
diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 0000000..1348feb
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1,3 @@
+docutils>=0.20
+sphinx>=7.0.1,<9
+sphinxcontrib-doxylink~=1.13