[ci] Cache runtime and compiler only for test runs (#32608)

We only need the compiler built for `yarn test` in the root directory.
Rather than always cache both for every step, let's just do it where
it's needed explicitly.
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[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32608).
* #32609
* __->__ #32608

scripts/react-compiler/build-compiler.sh

@@ -11,5 +11,4 @@ if [[ "$REACT_CLASS_EQUIVALENCE_TEST" == "true" ]]; then
 fi
 
 echo "Building babel-plugin-react-compiler..."
-yarn --cwd compiler install --frozen-lockfile
 yarn --cwd compiler workspace babel-plugin-react-compiler build --dts