chore: fix maintainer email typo in flake.nix, harden coverage.sh (#449)

- Fix typo: mgail.com → gmail.com in flake.nix maintainer metadata
- Add -u (undefined vars) and -o pipefail to coverage.sh, consistent
  with version-sync.sh and tag-release.sh

.changeset/fix-nix-typo-and-scripts.md

@@ -0,0 +1,5 @@
+---
+"@googleworkspace/cli": patch
+---
+
+chore: fix maintainer email typo in flake.nix and harden coverage.sh

flake.nix

@@ -49,7 +49,7 @@
             description = cargoToml.package.description;
             homepage = cargoToml.package.homepage;
             license = licenses.asl20;
-            maintainers = [{ name = "Justin Poehnelt"; email = "justin.poehnelt@mgail.com"; }];
+            maintainers = [{ name = "Justin Poehnelt"; email = "justin.poehnelt@gmail.com"; }];
             mainProgram = "gws";
           };
         };

scripts/coverage.sh

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-set -e
+set -euo pipefail
 
 # Check if cargo-llvm-cov is installed
 if ! cargo llvm-cov --version &> /dev/null; then