Speed up pyN-check-uc jobs

...by skipping actual installation. We only need to check if they are
co-installable via metadata. We don't need to actually install them.

This will make the job much easier to run in environments where bindep
hasn't been run.

Change-Id: Iaa7f02ec9d1e734884b1329e2b177964f54d64df
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

tox.ini

@@ -13,23 +13,27 @@ commands =
 
 [testenv:py310-check-uc]
 basepython = python3.10
-deps = -r{toxinidir}/upper-constraints.txt
-commands = python -c 'print("done")'
+skip_install = true
+deps =
+commands = python -m pip install --dry-run -r{toxinidir}/upper-constraints.txt
 
 [testenv:py311-check-uc]
 basepython = python3.11
-deps = -r{toxinidir}/upper-constraints.txt
-commands = python -c 'print("done")'
+skip_install = true
+deps =
+commands = {[testenv:py310-check-uc]commands}
 
 [testenv:py312-check-uc]
 basepython = python3.12
-deps = -r{toxinidir}/upper-constraints.txt
-commands = python -c 'print("done")'
+skip_install = true
+deps =
+commands = {[testenv:py310-check-uc]commands}
 
 [testenv:py313-check-uc]
 basepython = python3.13
-deps = -r{toxinidir}/upper-constraints.txt
-commands = python -c 'print("done")'
+skip_install = true
+deps =
+commands = {[testenv:py310-check-uc]commands}
 
 [testenv:venv]
 commands = {posargs}