TST: Fix devdeps

pyproject.toml

@@ -1,6 +1,5 @@
 [build-system]
 requires = ["setuptools>=30.3.0",
             "setuptools_scm",
-            "wheel",
-            "numpy>=1.25,<2"]
+            "numpy>=1.25"]
 build-backend = "setuptools.build_meta"

tox.ini

@@ -5,13 +5,10 @@ envlist =
     twine
     bandit
     linkcheck
-requires =
-    setuptools >= 30.3.0
-    pip >= 19.3.1
 
 [testenv]
 setenv =
-    devdeps: PIP_EXTRA_INDEX_URL = https://pypi.anaconda.org/astropy/simple https://pypi.anaconda.org/scientific-python-nightly-wheels/simple
+    devdeps: PIP_EXTRA_INDEX_URL = https://pypi.anaconda.org/astropy/simple https://pypi.anaconda.org/liberfa/simple https://pypi.anaconda.org/scientific-python-nightly-wheels/simple
 
 # Pass through the following environemnt variables which are needed for the CI
 passenv = HOME,WINDIR,CC,CI
@@ -47,6 +44,7 @@ deps =
     # or nightly wheel of key dependencies.
     devdeps: numpy>=0.0.dev0
     devdeps: scipy>=0.0.dev0
+    devdeps: pyerfa>=0.0.dev0
     devdeps: astropy>=0.0.dev0
     devdeps: git+https://github.com/astropy/specutils.git@main#egg=specutils
 
@@ -56,6 +54,10 @@ extras =
     test
     alldeps: all
 
+install_command =
+    !devdeps: python -I -m pip install
+    devdeps: python -I -m pip install -v --pre
+
 commands =
     pip freeze
     !cov: pytest --pyargs synphot {toxinidir}/docs {posargs}