Fix cbmc-update CI job

We had a spurious update attempt logged in model-checking#3155 for the job prior to
this fix would empty out the version strings. This was caused by use of
undefined variables.

Resolves: model-checking#3155

.github/workflows/cbmc-update.yml

@@ -30,7 +30,7 @@ jobs:
         env:
           GH_TOKEN: ${{ github.token }}
         run: |
-          grep ^CBMC_VERSION kani-dependencies >> $GITHUB_ENV
+          grep ^CBMC_VERSION kani-dependencies | sed 's/"//g' >> $GITHUB_ENV
           CBMC_LATEST=$(gh -R diffblue/cbmc release list | grep Latest | awk '{print $1}' | cut -f2 -d-)
           echo "CBMC_LATEST=$CBMC_LATEST" >> $GITHUB_ENV
           # check whether the version has changed at all
@@ -47,8 +47,8 @@ jobs:
           elif ! git ls-remote --exit-code origin cbmc-$CBMC_LATEST ; then
             CBMC_LATEST_MAJOR=$(echo $CBMC_LATEST | cut -f1 -d.)
             CBMC_LATEST_MINOR=$(echo $CBMC_LATEST | cut -f2 -d.)
-            sed -i "s/^CBMC_MAJOR=.*/CBMC_MAJOR=\"$CBMC_MAJOR\"/" kani-dependencies
-            sed -i "s/^CBMC_MINOR=.*/CBMC_MINOR=\"$CBMC_MINOR\"/" kani-dependencies
+            sed -i "s/^CBMC_MAJOR=.*/CBMC_MAJOR=\"$CBMC_LATEST_MAJOR\"/" kani-dependencies
+            sed -i "s/^CBMC_MINOR=.*/CBMC_MINOR=\"$CBMC_LATEST_MINOR\"/" kani-dependencies
             sed -i "s/^CBMC_VERSION=.*/CBMC_VERSION=\"$CBMC_LATEST\"/" kani-dependencies
             git diff
             if ! ./scripts/kani-regression.sh ; then