chore: dotnet 4.1.1 release using only mpl-1.7.6

[imabhichow]

Issue #, if available:

Description of changes:

• Release ESDK dotnet by only updating MPL version 'ESDK.csproj' and not bumping to the MPL dotnet commit.
• See chore(dotnet): prepare for 4.1.1 release #830 for CI checks when a submodule is updated to MPL dotnet commit.
  • All checks pass except Codegen on chore(dotnet): prepare for 4.1.1 release #830 will fail while MPL polymorph, because MPL dotnet and ESDK dotnet base have different smithy dafny.

Squash/merge commit message, if applicable:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.