pbr, gitpython, gerrit: migrate to Python 3.9 and 3.10

Remove the older Python versions from the recipes.

dev-python/gitpython/gitpython-3.1.27.recipe

@@ -21,8 +21,8 @@ BUILD_REQUIRES="
 	haiku_devel
 	"
 
-PYTHON_PACKAGES=(python3)
-PYTHON_VERSIONS=(3.7)
+PYTHON_PACKAGES=(python39 python310)
+PYTHON_VERSIONS=(3.9 3.10)
 for i in "${!PYTHON_PACKAGES[@]}"; do
 pythonPackage=${PYTHON_PACKAGES[i]}
 pythonVersion=${PYTHON_VERSIONS[$i]}