[2] Track repo rule label attributes after the first non-existent one

Even with this commit, the fact that a particular label in a repository
rule's label attributes does not resolve to a regular file is not
tracked, which means that there is still a potential for incorrect
incremental fetches.

Work towards bazelbuild#13441

src/test/shell/bazel/external_integration_test.sh

@@ -2461,7 +2461,7 @@ EOF
 
   mkdir main
   cd main
-  cat > foo.bzl <<'EOF'
+  cat > foo.bzl <<EOF
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 def foo():
@@ -2471,7 +2471,7 @@ def foo():
     build_file = "@b//:a.BUILD",
   )
 EOF
-  cat > bar.bzl <<'EOF'
+  cat > bar.bzl <<EOF
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 def bar():
@@ -2493,7 +2493,7 @@ EOF
   touch BUILD
 
   bazel build //... > "${TEST_log}" 2>&1 && fail "expected failure" || :
-  inplace-sed -e 's?$(pwd)/?PWD/?g' "${TEST_log}"
+  inplace-sed -e "s?$(pwd)/?PWD/?g" "${TEST_log}"
 
   expect_not_log '[iI]nternal [eE]rror'
   expect_not_log 'IllegalStateException'