Fix tests: Remove constraints

This fixes: Some possibly relevant errors from pip install:
    ERROR: Could not open requirements file: [Errno 2] No such file or directory: '.github/workflows/constraints.txt'
Error installing poetry.

.github/workflows/release.yml

@@ -22,12 +22,12 @@ jobs:
 
       - name: Upgrade pip
         run: |
-          pip install --constraint=.github/workflows/constraints.txt pip
+          pip install pip
           pip --version
 
       - name: Install Poetry
         run: |
-          pip install --constraint=.github/workflows/constraints.txt poetry
+          pip install poetry
           poetry --version
 
       - name: Check if there is a parent commit

.github/workflows/tests.yml

@@ -45,7 +45,7 @@ jobs:
 
       - name: Upgrade pip
         run: |
-          pip install --constraint=.github/workflows/constraints.txt pip
+          pip install pip
           pip --version
 
       - name: Upgrade pip in virtual environments
@@ -59,13 +59,13 @@ jobs:
 
       - name: Install Poetry
         run: |
-          pipx install --pip-args=--constraint=.github/workflows/constraints.txt poetry
+          pipx install poetry
           poetry --version
 
       - name: Install Nox
         run: |
-          pipx install --pip-args=--constraint=.github/workflows/constraints.txt nox
-          pipx inject --pip-args=--constraint=.github/workflows/constraints.txt nox nox-poetry
+          pipx install nox
+          pipx inject nox nox-poetry
           nox --version
 
       - name: Install ghostscript
@@ -130,18 +130,18 @@ jobs:
 
       - name: Upgrade pip
         run: |
-          pip install --constraint=.github/workflows/constraints.txt pip
+          pip install pip
           pip --version
 
       - name: Install Poetry
         run: |
-          pipx install --pip-args=--constraint=.github/workflows/constraints.txt poetry
+          pipx install poetry
           poetry --version
 
       - name: Install Nox
         run: |
-          pipx install --pip-args=--constraint=.github/workflows/constraints.txt nox
-          pipx inject --pip-args=--constraint=.github/workflows/constraints.txt nox nox-poetry
+          pipx install nox
+          pipx inject nox nox-poetry
           nox --version
 
       - name: Download coverage data
@@ -158,4 +158,4 @@ jobs:
           nox --session=coverage -- xml -i
 
       - name: Upload coverage report
-        uses: codecov/[email protected]
+        uses: codecov/[email protected]