Clean up some yaml mistakes (#16300)

# Objective

Our build pipeline should have no grammar or syntax mistakes.

## Solution

Remove a reference to a non-existent variable and clean up the taplo
`echo`s.

.github/workflows/ci.yml

@@ -230,10 +230,10 @@ jobs:
       - name: Taplo info
         if: failure()
         run: |
-          echo 'To fix toml fmt, please run `taplo fmt`'
-          echo 'To check for a diff, run `taplo fmt --check --diff'
+          echo 'To fix toml fmt, please run `taplo fmt`.'
+          echo 'To check for a diff, run `taplo fmt --check --diff`.'
           echo 'You can find taplo here: https://taplo.tamasfe.dev/'
-          echo 'Or if you use VSCode, use the `Even Better Toml` extension with 2 spaces'
+          echo 'Or if you use VSCode, use the `Even Better Toml` extension.'
           echo 'You can find the extension here: https://marketplace.visualstudio.com/items?itemName=tamasfe.even-better-toml'
 
   typos:

.github/workflows/validation-jobs.yml

@@ -31,7 +31,7 @@ jobs:
         with:
           path: |
             target
-          key: ${{ runner.os }}-ios-install-${{ matrix.toolchain }}-${{ hashFiles('**/Cargo.lock') }}
+          key: ${{ runner.os }}-ios-install-${{ hashFiles('**/Cargo.lock') }}
 
       # TODO: remove x86 target once it always run on arm GitHub runners
       - name: Add iOS targets