ci: Only install sccache action once per workflow (#2123)

* ci: Disable sccache on Windows again

Because for some reason today, the action doesn't install:
```
Error: Error: File was unable to be removed Error: EBUSY: resource busy or locked, rmdir 'C:\hostedtoolcache\windows\sccache\0.8.1\x64'
Error: File was unable to be removed Error: EBUSY: resource busy or locked, rmdir 'C:\hostedtoolcache\windows\sccache\0.8.1\x64'
```

* Check if it's installed already

* Fix

.github/actions/nss/action.yml

@@ -60,6 +60,10 @@ runs:
         echo "BUILD_NSS=0" >> "$GITHUB_ENV"
 
     - name: Use sccache
+      # Apparently the action can't be installed twice in the same workflow, so check if
+      # it's already installed by checking if the RUSTC_WRAPPER environment variable is set
+      # (which every "use" of this action needs to therefore set)
+      if: env.RUSTC_WRAPPER != 'sccache'
       uses: mozilla-actions/sccache-action@2e7f9ec7921547d4b46598398ca573513895d0bd # v0.0.4
 
     - name: Enable sscache

.github/actions/rust/action.yml

@@ -34,6 +34,10 @@ runs:
         targets: ${{ inputs.targets }}
 
     - name: Use sccache
+      # Apparently the action can't be installed twice in the same workflow, so check if
+      # it's already installed by checking if the RUSTC_WRAPPER environment variable is set
+      # (which every "use" of this action needs to therefore set)
+      if: env.RUSTC_WRAPPER != 'sccache'
       uses: mozilla-actions/sccache-action@2e7f9ec7921547d4b46598398ca573513895d0bd # v0.0.4
 
     - name: Enable sscache