patch 8.2.2507: github build may fail if Ubuntu 20.04 is used

Problem:    Github build may fail if Ubuntu 20.04 is used.  Installing rust is
            not needed.
Solution:   Specify ubuntu-18.04 instead of latest. Update "pip" instead of
            installing rust. (Ozaki Kiichi, closes #7820)

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   linux:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     env:
       CC: ${{ matrix.compiler }}
@@ -207,8 +207,8 @@ jobs:
           COVERALLS_PARALLEL: true
           TRAVIS_JOB_ID: ${{ github.run_id }}
         run: |
-          sudo apt-get install -y python3-setuptools python3-wheel rustc
-          pip3 install --user setuptools-rust
+          sudo apt-get install -y python3-setuptools python3-wheel
+          sudo -H pip3 install pip -U
           # needed for https support for coveralls building cffi only works with gcc, not with clang
           CC=gcc pip3 install --user cpp-coveralls pyopenssl ndg-httpsclient pyasn1
           ~/.local/bin/coveralls -b "${SRCDIR}" -x .xs -e "${SRCDIR}"/if_perl.c -e "${SRCDIR}"/xxd -e "${SRCDIR}"/libvterm --encodings utf-8
@@ -228,7 +228,7 @@ jobs:
           done
 
   coveralls:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     needs: linux
     if: always() && github.event_name != 'pull_request'

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2507,
 /**/
     2506,
 /**/