docs+test: fix remaining installer downloads without -L (#4006)

Co-authored-by: lf- <lf-@users.noreply.github.com>

doc/manual/src/release-notes/rl-1.7.md

@@ -117,7 +117,7 @@ features:
   - The binary tarball installer has been improved. You can now install
     Nix by running:
     
-        $ bash <(curl https://nixos.org/nix/install)
+        $ bash <(curl -L https://nixos.org/nix/install)
 
   - More evaluation errors include position information. For instance,
     selecting a missing attribute will print something like

doc/manual/src/release-notes/rl-2.1.md

@@ -10,7 +10,7 @@ in certain situations. In addition, it has the following new features:
   - The Nix installer now supports performing a Multi-User
     installation for Linux computers which are running systemd. You
     can select a Multi-User installation by passing the `--daemon`
-    flag to the installer: `sh <(curl https://nixos.org/nix/install)
+    flag to the installer: `sh <(curl -L https://nixos.org/nix/install)
     --daemon`.
 
     The multi-user installer cannot handle systems with SELinux. If

tests/install-darwin.sh

@@ -53,7 +53,7 @@ trap finish EXIT
 
 # First setup Nix
 cleanup
-curl -o install https://nixos.org/nix/install
+curl -L -o install https://nixos.org/nix/install
 yes | bash ./install
 verify