Do not install editable NNCF in workflows (#2054)

### Changes
Now doing `pip install .` instead of `pip install -e .` in GH Actions
workflow files.

### Reason for changes
Ubuntu 22 and pip/setuptools have a lot of bugs when installing editable
packages with the new build isolation flow (e.g. when the pyproject.toml
is present). We don't have pyproject.toml yet, but should we need to
switch, better to have less failures in the unrelated tests and
workflows - we don't really need editability in GH actions we have now.

### Related tickets

N/A

### Tests
Can only test changes in these workflows post-factum.

.github/workflows/build_html_doc.yml

@@ -15,7 +15,7 @@ jobs:
           ref: ${{ inputs.ref }}
       - name: Install NNCF and doc requirements
         run: |
-          pip install -e .
+          pip install .
           pip install -r docs/api/requirements.txt
       - name: Build API docs
         run: |

.github/workflows/build_schema_page.yml

@@ -11,7 +11,7 @@ jobs:
       - name: Install and Build
         run: |
           pip install json-schema-for-humans
-          pip install -e .
+          pip install .
           python -c 'import jstyleson; from nncf.config import NNCFConfig; jstyleson.dump(NNCFConfig.schema(), open("./schema.json", "w"), indent=2)'
           mkdir schema
           generate-schema-doc --deprecated-from-description schema.json schema/index.html