better long-term control of valid astropy versions (PR#17402)

(cherry picked from commit ff061ba)

tox.ini

@@ -22,7 +22,7 @@ passenv =
     TMPDIR
 conda_deps =
     asdf>=2.7,!=2.10.0
-    astropy>=4.3,!=5.3.0
+    astropy>=4.3,!=5.3.0,!=6.1.5,!=6.1.6,!=7.0.0
     astroquery>=0.4
     astroscrappy>=1.1
     bokeh>=3.0
@@ -48,9 +48,9 @@ conda_deps =
     scipy>=1.3
     sextractor>=2.8.6
     specutils>=1.1
-    sqlalchemy>=1.3,<2.0.0a0  # new v2 API breaks calmgr (which is a wheel)
+    sqlalchemy>=1.3,<2.0.0a0  # new v2 API breaks calmgr (installed as wheel)
 conda_channels =
-    http://jastro.org/astroconda/public
+    http://astroconda.gemini.edu/public
     conda-forge
 conda_create_args =
     --override-channels