Test with PHP8.0

[phil-davis]

1. sort out variables in .travis.yml for selecting to run php-cs-fixer, phpunit and phpstan
2. Add a matrix entry to run just phpunit on Ubuntu 20.04 "focal" with "nightly" PHP (which is the way to get PHP 8.0 at the moment) Note: focal does not have postgresql available by default, so addons postgresql needs to be specified in .travis.yml
3. When not running php-cs-fixer, explicitly remove it from composer.json (because php-cs-fixer does not yet support PHP 8.0, so composer cannot sort out dependencies if we have PHP 8.0 and php-cs-fixer 2.* together)
4. Remove default value from oldObject parameter to processICalendarChange
   fixes error https://travis-ci.org/github/sabre-io/dav/jobs/732659316

1) Sabre\CalDAV\Schedule\DeliverNewEventTest::testDelivery
Required parameter $newObject follows optional parameter $oldObject
/home/travis/build/sabre-io/dav/lib/CalDAV/Schedule/Plugin.php:612
/home/travis/build/sabre-io/dav/tests/Sabre/DAVServerTest.php:144
/home/travis/build/sabre-io/dav/tests/Sabre/DAVServerTest.php:119
/home/travis/build/sabre-io/dav/tests/Sabre/CalDAV/Schedule/DeliverNewEventTest.php:19

[codecov]

Codecov Report

Merging #1296 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1296      +/-   ##
============================================
+ Coverage     97.12%   97.14%   +0.01%     
- Complexity     2774     2792      +18     
============================================
  Files           174      174              
  Lines          8028     8117      +89     
============================================
+ Hits           7797     7885      +88     
- Misses          231      232       +1     

Impacted Files	Coverage Δ	Complexity Δ
lib/CalDAV/Schedule/Plugin.php	99.23% <100.00%> (+0.01%)	100.00 <11.00> (ø)
lib/DAV/Server.php	96.13% <0.00%> (-0.18%)	192.00% <0.00%> (ø%)
lib/CardDAV/Card.php	100.00% <0.00%> (ø)	18.00% <0.00%> (ø%)
lib/DAVACL/FS/File.php	100.00% <0.00%> (ø)	3.00% <0.00%> (ø%)
lib/DAV/Sync/Plugin.php	100.00% <0.00%> (ø)	26.00% <0.00%> (ø%)
lib/DAVACL/Principal.php	100.00% <0.00%> (ø)	17.00% <0.00%> (ø%)
lib/CalDAV/CalendarHome.php	100.00% <0.00%> (ø)	44.00% <0.00%> (+1.00%)
lib/CalDAV/CalendarObject.php	100.00% <0.00%> (ø)	19.00% <0.00%> (ø%)
lib/CalDAV/Schedule/Inbox.php	100.00% <0.00%> (ø)	10.00% <0.00%> (ø%)
lib/CalDAV/Schedule/Outbox.php	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
... and 31 more

---

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[phil-davis]

https://travis-ci.org/github/sabre-io/dav/jobs/732560846
psql: error: could not connect to server: could not connect to server: No such file or directory

ToDo: look at what is needed to make postgresql start on Ubuntu 20.04 "focal" on Travis.

[phil-davis]

The one code change needed is exactly the same type of thing that was needed in other repos. Nothing really exciting to review here - I will merge.