Revert "Only run error code explanation removal check if on CI"

This reverts commit d6962ff.

Author: pietroalbini

src/ci/docker/host-x86_64/mingw-check/validate-error-codes.sh

@@ -1,12 +1,7 @@
 #!/bin/bash
 # Checks that no error code explanation is removed.
 
-set -eo pipefail
-
-if [[ -z "$BASE_COMMIT" ]]; then
-    echo "not checking error code explanations removal"
-    exit 0
-fi
+set -euo pipefail
 
 echo "Check if an error code explanation was removed..."
 

src/ci/docker/run.sh

@@ -219,13 +219,9 @@ else
   command="/checkout/src/ci/run.sh"
 fi
 
-if [ "$CI" != "" ]; then
-    # Get some needed information for $BASE_COMMIT
-    git fetch "https://github.com/$GITHUB_REPOSITORY" "$GITHUB_BASE_REF"
-    BASE_COMMIT="$(git merge-base FETCH_HEAD HEAD)"
-else
-    BASE_COMMIT=""
-fi
+# Get some needed information for $BASE_COMMIT
+git fetch "https://github.com/$GITHUB_REPOSITORY" "$GITHUB_BASE_REF"
+BASE_COMMIT="$(git merge-base FETCH_HEAD HEAD)"
 
 docker \
   run \