Bump Npgsql in /src/providers/WorkflowCore.Persistence.PostgreSQL

Bumps [Npgsql](https://github.com/npgsql/npgsql) from 5.0.14 to 5.0.18.
- [Release notes](https://github.com/npgsql/npgsql/releases)
- [Commits](npgsql/npgsql@v5.0.14...v5.0.18)

---
updated-dependencies:
- dependency-name: Npgsql
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

src/providers/WorkflowCore.Persistence.PostgreSQL/WorkflowCore.Persistence.PostgreSQL.csproj

@@ -47,7 +47,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.1'">
-    <PackageReference Include="Npgsql" Version="5.0.14" />
+    <PackageReference Include="Npgsql" Version="5.0.18" />
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="5.0.1" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="5.0.1">
       <PrivateAssets>All</PrivateAssets>