fix: Add exclude+include for EPAS 18 PostGIS matrix to fix empty runs-on

The previous include entry for pgver 18 with postgisver 35 did not match
any existing matrix combination (postgisver 34 != 35), so GitHub Actions
created a new entry without an os value, causing runs-on to evaluate to ''.

Use exclude to remove pgver 18 / postgisver 34 combos, then include with
explicit os to re-add them with postgisver 35.

Author: asheshv

.github/workflows/run-python-tests-epas.yml

@@ -34,8 +34,15 @@ jobs:
         os: [ubuntu-22.04, windows-latest]
         pgver: [14, 15, 16, 17, 18]
         postgisver: [34]
-        include:
+        exclude:
           - pgver: 18
+            postgisver: 34
+        include:
+          - os: ubuntu-22.04
+            pgver: 18
+            postgisver: 35
+          - os: windows-latest
+            pgver: 18
             postgisver: 35
 
     runs-on: ${{ matrix.os }}