Fix GN task on nightly

Author: Manishearth

.github/workflows/build-test.yml

@@ -889,7 +889,7 @@ jobs:
     # then this line is no longer needed.
     - uses: actions-rs/toolchain@v1
       with:
-        toolchain: ${{ env.INSTALLED_NIGHTLY_VERSION }}
+        toolchain: $INSTALLED_NIGHTLY_VERSION
         override: true
 
     - name: Run the example with dhat-rs to collect memory information

ffi/gn/.cargo/config

@@ -3,7 +3,6 @@
 # (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
 # AUTO-GENERATED in ffi.toml
-
 [source.crates-io]
 replace-with = "vendored-sources"
 

tools/scripts/gn.toml

@@ -60,11 +60,13 @@ cd ffi/gn
 
 rm -rf vendor
 output = exec --fail-on-error cargo vendor
+output_trimmed = trim_start ${output.stdout} # Needed since there are whitespace differences between cargo versions
+                                             # Probably can be removed when we update our CI stable
 writefile .cargo/config "# This file is part of ICU4X. For terms of use, please see the file\n"
 appendfile .cargo/config "# called LICENSE at the top level of the ICU4X source tree\n"
 appendfile .cargo/config "# (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).\n\n"
 appendfile .cargo/config "# AUTO-GENERATED in ffi.toml\n"
-appendfile .cargo/config ${output.stdout}
+appendfile .cargo/config ${output_trimmed}
 '''
 
 [tasks.gn-gen]