build: partially revert AzCopy changes from 22c509f (#19092)

When we first transitioned to the `R1` network isolation
environment--which required us to _not_ contact
powershellgallery.com--we had to give up on the `AzureFileCopy` task.

Since then, the `AzurePowerShell` task has also become somewhat broken
while OneBranch fixed the issue that prevented us from using
`AzureFileCopy`.

In short, we now need to:

- Install the Azure PowerShell modules directly from our own feed (which
satisfies the network constraint)
- ... using `PSResourceGet` ...
- ... for Windows PowerShell 5.1 ...
- which is used by `AzureFileCopy` to later perform authentication.

.github/actions/spelling/expect/expect.txt

@@ -78,7 +78,6 @@ autoscrolling
 Autowrap
 AVerify
 awch
-AZCOPY
 azurecr
 AZZ
 backgrounded
@@ -1342,7 +1341,6 @@ PROPTITLE
 propvar
 propvariant
 psa
-PSCRED
 PSECURITY
 pseudoconsole
 psh